First Aid for the USMLE Step 1 (2021)

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Build your confidence with First Aid for the USMLE Step 1 (2021), a must-have for certification seekers.

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FOR
THE®
New York / Chicago / San Francisco / Athens / London / Madrid / Mexico City
Milan / New Delhi / Singapore / Sydney / Toronto
USMLE
STEP 1
2021
FIRST AID
TAO LE, MD, MHS
Founder, ScholarRx
Associate Clinical Professor, Department of Medicine
University of Louisville School of Medicine
VIKAS BHUSHAN, MD
Founder, First Aid for the USMLE Step 1
Boracay, Philippines
MATTHEW SOCHAT, MD
Physician, Hematology/Oncology
Southeastern Medical Oncology Center
KRISTINA DAMISCH, MD
University of Iowa Carver College of Medicine
Class of 2020
JORDAN ABRAMS, MD
Resident, Department of Anesthesiology,
Perioperative and Pain Medicine
Mount Sinai West and Mount Sinai Morningside Hospitals
KIMBERLY KALLIANOS, MD
Assistant Professor, Department of Radiology and Biomedical Imaging
University of California, San Francisco School of Medicine
HUMOOD BOQAMBAR, MB BCh BAO
Assistant Registrar, Department of Orthopedic Surgery
Farwaniya Hospital
CONNIE QIU
Lewis Katz School of Medicine at Temple University
MD/PhD Candidate
CAROLINE COLEMAN, MD
Resident, Department of Medicine
Emory University School of Medicine

First Aid for the® USMLE Step 1 2021: A Student-to-Student Guide
Copyright © 2021 by Tao Le and Vikas Bhushan. All rights reserved. Printed in the United States of America. Except as
permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distrib-
uted in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of
the publisher.
Previous editions copyright © 1991 through 2020 by Tao Le and Vikas Bhushan. First edition copyright © 1990, 1989
by Vikas Bhushan, Jeffrey Hansen, and Edward Hon.
Photo and line art credits for this book begin on page 753 and are considered an extension of this copyright page.
Portions of this book identified with the symbol are copyright © USMLE-Rx.com (MedIQ Learning, LLC).
Portions of this book identified with the symbol are copyright © Dr. Richard Usatine.
Portions of this book identified with the symbol are under license from other third parties. Please refer to page 753
for a complete list of those image source attribution notices.
First Aid for the® is a registered trademark of McGraw Hill.
1 2 3 4 5 6 7 8 9 LMN 25 24 23 22 21 20
ISBN 978-1-260-46752-9
MHID 1-260-46752-X
Notice
Medicine is an ever-changing science. As new research and clinical experience broaden our knowledge,
changes in treatment and drug therapy are required. The authors and the publisher of this work have checked
with sources believed to be reliable in their efforts to provide information that is complete and generally in
accord with the standards accepted at the time of publication. However, in view of the possibility of human
error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been
involved in the preparation or publication of this work warrants that the information contained herein is in
every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the
results obtained from use of the information contained in this work. Readers are encouraged to confirm the
information contained herein with other sources. For example and in particular, readers are advised to check
the product information sheet included in the package of each drug they plan to administer to be certain
that the information contained in this work is accurate and that changes have not been made in the recom-
mended dose or in the contraindications for administration. This recommendation is of particular importance
in connection with new or infrequently used drugs.
This book was set in Electra LT Std by GW Inc.
The editors were Bob Boehringer and Christina M. Thomas.
Project management was provided by GW Inc.
The production supervisor was Jeffrey Herzich.
LSC Communications was printer and binder.
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Copyright © 2021. Exclusive rights by McGraw Hill for manufacture and export. This book cannot be reexported from
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v
Contents
Contributing Authors vii
Associate Authors viii
Faculty Advisors ix
Foreword xi
Preface xiii
Special Acknowledgments xiv
General Acknowledgments xv
How to Contribute xvii
How to Use This Book xix
Selected USMLE Laboratory Values xx
First Aid Checklist for the USMLE Step 1 xxii
`` S E C T I O N I G U I D E TO E F F I C I E N T E X A M P R E PA R AT I O N 1
Introduction 2
USMLE Step 1—The Basics 2
Defining Your Goal 12
Learning Strategies 13
Timeline for Study 16
Study Materials 20
Test-Taking Strategies 22
Clinical Vignette Strategies 23
If You Think You Failed 24
Testing Agencies 25
References 25
`` S E C T I O N I S U P P L E M E N T S P E C I A L S I T UAT I O N S 27
`` S E C T I O N I I H I G H - Y I E L D G E N E R A L P R I N C I P L E S 29
How to Use the Database 30
Biochemistry 33
Immunology 95
Microbiology 123
Pathology 205
Pharmacology 231
Public Health Sciences 259

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vi
`` S E C T I O N I I I H I G H - Y I E L D O R G A N S YS T E M S 283
Approaching the Organ Systems 284
Cardiovascular 287
Endocrine 333
Gastrointestinal 367
Hematology and Oncology 413
Musculoskeletal, Skin, and Connective Tissue 455
Neurology and Special Senses 503
Psychiatry 575
Renal 601
Reproductive 635
Respiratory 683
Rapid Review 713
`` S E C T I O N I V TO P - R AT E D R E V I E W R E S O U R C E S 737
How to Use the Database 738
Question Banks 740
Web and Mobile Apps 740
Comprehensive 741
Anatomy, Embryology, and Neuroscience 741
Behavioral Science 742
Biochemistry 742
Cell Biology and Histology 743
Microbiology and Immunology 743
Pathology 743
Pharmacology 744
Physiology 744
``
Abbreviations and Symbols 745
Image Acknowledgments 753
Index 775
About the Editors 842

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vii
Contributing Authors
LILIT ASLANYAN, DO
Resident, Department of Medicine
New York University Winthrop Hospital
ANUP CHALISE, MBBS
Resident, Department of General Surgery
Nepal Medical College and Teaching Hospital
WEELIC CHONG
Sidney Kimmel Medical College at Thomas Jefferson University
MD/PhD Candidate
PANAGIOTIS KAPARALIOTIS, MD
Resident, Department of Pathology
St. Sophia’s Children’s Hospital, Greece
MITCHELL A. KATONA, MD, MPH
Resident, Division of Emergency Medicine
Dell Medical School
ANDREA LEAL LOPEZ, MD
ITESM School of Medicine Ignacio A. Santos, Mexico
VASILY OVECHKO, MD
Resident, Department of Pediatric Oncology
Dmitry Rogachev National Medical Research Center of Pediatric
Hematology, Oncology and Immunology
VIVEK PODDER, MBBS
Tairunnessa Memorial Medical College and Hospital, Bangladesh
ROHAN BIR SINGH, MD
Fellow, Department of Ophthalmology
Massachusetts Eye and Ear, Harvard Medical School
Image and IllustratIon team
YOOREE GRACE CHUNG
Emory University School of Medicine
MD/PhD Candidate
STEPHANIE JONES, PhD
Emory University Laney Graduate School
VICTOR JOSE MARTINEZ LEON, MD
Resident, Department of Medicine
Einstein Medical Center Philadelphia
ANGEL XIAO, MSE
Emory University School of Medicine
Class of 2022
ALIREZA ZANDIFAR, MD
Research Fellow, Department of Radiology
Children’s Hospital of Philadelphia

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viii
Associate Authors
ERIC L. BARASH
Wake Forest School of Medicine
Class of 2022
LAUREN CLAUS
Johns Hopkins University School of Medicine
Class of 2021
CHRISTIAN FAABORG-ANDERSEN
Emory University School of Medicine
Class of 2022
ELIE FLATOW
Touro College of Osteopathic Medicine - Harlem
Class of 2021
SAMIRA RAHIM IBRAHIM
West Virginia School of Osteopathic Medicine
Class of 2021
TROY KLEBER
Emory University School of Medicine
MD/MSCR Candidate
MARGARET C. SLACK
University of Washington School of Medicine
Class of 2022
REBECCA H. YU
Saba University School of Medicine
Class of 2022
MATTHEW WELLS, DO
Resident, Department of Orthopedic Surgery
William Beaumont Army Medical Center
SEAN EVANS
Emory University School of Medicine
Class of 2022
Image and IllustratIon team

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ix
Faculty Advisors
DIANA ALBA, MD
Assistant Professor, Division of Endocrinology, Diabetes, and Metabolism
University of California, San Francisco School of Medicine
MARK A.W. ANDREWS, PhD
Professor of Physiology
Lake Erie College of Osteopathic Medicine at Seton Hill
MARIA ANTONELLI, MD
Assistant Professor, Division of Rheumatology
MetroHealth Medical Center, Case Western Reserve University
HERMAN SINGH BAGGA, MD
Urologist, Allegheny Health Network
University of Pittsburgh Medical Center Passavant
SHIN C. BEH, MD
Assistant Professor, Department of Neurology & Neurotherapeutics
UT Southwestern Medical Center at Dallas
CARRIE BOHNERT, MPA
Standardized Patient Educator
SHELDON CAMPBELL, MD, PhD
Professor of Laboratory Medicine
Yale School of Medicine
BROOKS D. CASH, MD
Chief, Gastroenterology, Hepatology, and Nutrition
University of Texas Health Science Center at Houston
DIMITRI CASSIMATIS, MD
Associate Professor, Department of Medicine
Emory University School of Medicine
CATHERINE CHILES, MD
Associate Clinical Professor of Psychiatry
Yale School of Medicine
BRADLEY COLE, MD
Assistant Professor of Neurology
Loma Linda University School of Medicine
SAKINA FARHAT, MD
Consultant Gastroenterologist and Hepatologist
State University of New York Downstate Medical Center
CONRAD FISCHER, MD
Associate Professor, Medicine, Physiology, and Pharmacology
Touro College of Medicine
RAYUDU GOPALAKRISHNA, PhD
Associate Professor, Department of Integrative Anatomical Sciences
Keck School of Medicine of University of Southern California
MEREDITH K. GREER, MD
Fellow, Department of Medicine
Emory University School of Medicine
SUSAN HADLER, MD, MS
Professor Emerita of Pathology and Laboratory Medicine
University of North Carolina School of Medicine
MELANIE SCHORR HAINES, MD
Assistant Professor, Department of Medicine
Harvard Medical School
AMBER J. HECK, PhD
Associate Professor, Department of Medical Education
TCU and UNTHSC School of Medicine
JEFFREY W. HOFMANN, MD, PhD
Fellow, Department of Pathology
University of California, San Francisco School of Medicine
CLARK KEBODEAUX, PharmD
Clinical Associate Professor, Pharmacy Practice and Science
University of Kentucky College of Pharmacy
KRISTINE KRAFTS, MD
Assistant Professor, Department of Basic Sciences
University of Minnesota School of Medicine
MATTHEW KRAYBILL, PhD
Clinical Neuropsychologist
Cottage Health, Santa Barbara, California
GERALD LEE, MD
Associate Professor, Departments of Pediatrics and Medicine
Emory University School of Medicine
KACHIU C. LEE, MD, MPH
Assistant Clinical Professor, Department of Dermatology
The Warren Alpert Medical School of Brown University

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WARREN LEVINSON, MD, PhD
Professor, Department of Microbiology and Immunology
University of California, San Francisco School of Medicine
JAMES LYONS, MD
Professor of Pathology and Family Medicine
Alabama College of Osteopathic Medicine
CARL MARFURT, PhD
Professor Emeritus, Department of Anatomy, Cell Biology and Physiology
Indiana University School of Medicine Northwest, Gary
PETER MARKS, MD, PhD
Center for Biologics Evaluation and Research
US Food and Drug Administration
DOUGLAS A. MATA, MD, MPH
Department of Pathology
Memorial Sloan Kettering Cancer Center
KRISTEN L. PAGEL, MD, MPH
Assistant Professor, Department of Psychiatry
University of Utah School of Medicine
VICKI M. PARK, PhD, MS
Assistant Dean
University of Tennessee College of Medicine
DIANE E.S. PAYNE, MD, MPT
Assistant Professor, Department of Orthopedic Surgery
Emory University School of Medicine
SOROUSH RAIS-BAHRAMI, MD
Associate Professor of Urology and Radiology
University of Alabama at Birmingham School of Medicine
RICHARD P. RAMONELL, MD
Fellow, Department of Medicine
Emory University School of Medicine
JOHN C. ROSE, DO
Clinical Instructor, Department of Anesthesiology
Mount Sinai Morningside-West
SASAN SAKIANI, MD
Professor, Department of Medicine
University of Maryland Medical Center
SHIREEN MADANI SIMS, MD
Chief, Division of Gynecology, Gynecologic Surgery, and Obstetrics
University of Florida School of Medicine
HOWARD M. STEINMAN, PhD
Assistant Dean, Biomedical Science Education
Albert Einstein College of Medicine
RICHARD P. USATINE, MD
Professor, Dermatology and Cutaneous Surgery
University of Texas Health Science Center San Antonio
TISHA WANG, MD
Associate Clinical Professor, Department of Medicine
David Geffen School of Medicine at UCLA
SYLVIA WASSERTHEIL-SMOLLER, PhD
Professor Emerita, Department of Epidemiology and Population Health
Albert Einstein College of Medicine
ADAM WEINSTEIN, MD
Associate Professor of Medical Education and Pediatric Nephrology
Geisel School of Medicine at Dartmouth
ABHISHEK YADAV, MBBS, MSc
Associate Professor of Anatomy
Geisinger Commonwealth School of Medicine
KRISTAL YOUNG, MD
Clinical Instructor, Department of Cardiology
Huntington Hospital, Pasadena, California
DONG ZHANG, PhD
Associate Professor of Biochemistry and Cancer Biology
New York Institute of Technology College of Osteopathic Medicine

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xi
Foreword
“If you see something that is not right, not fair, not just, you have a moral obligation to do something.”
Congressman John Lewis
First Aid for the USMLE Step 1 began over 30 years ago as a resource to prepare aspiring physicians for their first
medical board exam. Since then, it has become one of the most well-known textbooks used by medical students
worldwide. While we closely follow the USMLE’s lead in most respects, the widespread use of our book also provides
an opportunity for us to be leaders in medical education.
In prior editions, there has been an unfortunate absence of diversity in both the text and images. This year, we
strongly affirm that representing a broad spectrum of patients is essential for preparing for a successful medical
career. The practice of medicine is inextricably intertwined with social determinants of health, and sociocultural
understanding complements scientific knowledge for the future physician. Failing to provide representation of a
diversity of people limits the educational experience and is to the detriment of future patients. We here describe our
approach to improving the representation of race, ethnicity, sex, and gender, recognizing that we are neither experts
nor authorities on diversity, equity, and inclusion.
We first surveyed our existing visual depictions of patients and pathologies. Of nearly 70 illustrations showing skin
tone or sex in the 2020 edition, every single one showed pink/light beige skin, and all but one was male-appearing,
excluding reproductive anatomy illustrations. To address this lack of diversity, we revised our illustrations to better
reflect Fitzpatrick skin types I-VI and introduced more female-appearing and gender-neutral illustrations.
We also reviewed our use of language in the text. With respect to race and ethnicity, we transitioned from using
“African-American” to “Black,” as not all Black patients are American or have African ancestry. We now capitalize
“Black” in accordance with major journalistic organizations. We also switched from “Caucasian” to “White,” which
we hope will be more accurate and inclusive.
We found many opportunities to improve the language used to describe disabled and ill patients as well. We now
use person-first language such as “patients with diabetes” instead of “diabetic patients.” Dated references to “mental
retardation” have been replaced with “intellectual disability.” We also removed other stigmatizing terms such as
“alcoholics,” “smokers,” “epileptics,” and “bulimics” and replaced with appropriate person-first language.
Finally, we reviewed our use of terminology surrounding sex and gender identity. We opted for more neutral
language by changing most uses of gendered pronouns to “they/them/theirs,” as well as changing “mother” to
“pregnant patient.” We also removed gendered terms such as “girl,” “boy,” “woman,” and “man” in favor of “female”
and “male” when referring to biological sex.

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xii
We acknowledge that our approach is imperfect and challenges remain. We also recognize that there may be
differing perspectives that need to be addressed and balanced. However, just as the medical community learns
invaluable lessons from its patients, we greatly value input from our peers and colleagues. We enthusiastically
encourage feedback on our efforts to better represent all people. If you have comments or suggestions, please submit
them via our website at www.firstaidteam.com. Alternatively, you can email us at firstaid@scholarrx.com. Thank
you for your help in making First Aid for the USMLE Step 1 an increasingly inclusive and useful resource.
Louisville Tao Le
Boracay Vikas Bhushan
Goldsboro, NC Matthew Sochat
Kuwait Humood Boqambar
Iowa City Kristina Damisch
Philadelphia Connie Qiu
New York City Jordan Abrams
Atlanta Caroline Coleman
San Francisco Kimberly Kallianos

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xiii
Preface
With the 31st edition of First Aid for the USMLE Step 1, we continue our commitment to providing students with
the most useful and up-to-date preparation guide for the USMLE Step 1. This edition represents an outstanding
revision in many ways, including:
104 entirely new or heavily revised high-yield topics reflecting evolving trends in the USMLE Step 1.
Updated ethics section and introduction of new communications skills section to reflect the recently changed
Step 1 exam.
Extensive text revisions, new mnemonics, clarifications, and corrections curated by a team of 25 medical student
and resident physician authors who excelled on their Step 1 examinations and verified by a team of expert faculty
advisors and nationally recognized USMLE instructors.
Updated with 179 new and revised diagrams and illustrations as part of our ongoing collaboration with
USMLE-Rx and ScholarRx (MedIQ Learning, LLC).
Updated with 62 new and revised photos to help visualize various disorders, descriptive findings, and basic
science concepts. Additionally, revised imaging photos have been labeled and optimized to show both normal
anatomy and pathologic findings.
Updated exam preparation advice for USMLE Step 1 pass/fail, Step 1 blueprint changes, and COVID-19
impacts.
Revised language to support diversity, equity, and inclusion.
Updated study tips on the opening page of each chapter.
Improved organization and integration of text, illustrations, clinical images, and tables throughout for focused
review of high-yield topics.
Revised and expanded ratings of current, high-yield review resources, with clear explanations of their relevance
to USMLE review.
Real-time Step 1 updates and corrections can be found exclusively on our blog, www.firstaidteam.com.
We invite students and faculty to share their thoughts and ideas to help us continually improve First Aid for the
USMLE Step 1 through our blog and collaborative editorial platform. (See How to Contribute, p. xvii.)
Louisville Tao Le
Boracay Vikas Bhushan
Goldsboro, NC Matthew Sochat
Kuwait Humood Boqambar
Iowa City Kristina Damisch
Philadelphia Connie Qiu
New York City Jordan Abrams
Atlanta Caroline Coleman
San Francisco Kimberly Kallianos

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xiv
Special Acknowledgments
This has been a collaborative project from the start. We gratefully acknowledge the thousands of thoughtful
comments, corrections, and advice of the many medical students, international medical graduates, and faculty who
have supported the authors in our continuing development of First Aid for the USMLE Step 1.
We provide special acknowledgment and thanks to the following individuals who made exemplary contributions to
this edition through our voting, proofreading, and crowdsourcing platform: Moatasem Al-Janabi, Syeda Akila Ally,
Grigory Davidov, Harpreet Dhanjal, Lucia Dominguez, Chinedum Enete, Emma Fenske, Heather Finlay-Morreale,
Louna Ftouni, Margaret Ginoza, Fariah Asha Haque, E. Paige Hart, Zeid Hassan, I-Chun Hung, Karawan Hussein,
Urma Jalil, Dana Jorgenson, Alvin Jose, Alec Kacew, Clara Kerwin, Shaima Khandaker, Joanna Liao, Annalisa Lopez,
Freda Quimba Malanyaon, Jessica Marks, Juliana Maya, Tuba Mirza, Mardochere Morisset, Waneeza Mughees, Billis
Paras, Neesirg Patel, Gabrielle Pierce, Faateh Ahmad Rauf, Amitoz Saini, Danusha Sanchez, Andrea Sánchez, Emily
Charlotte Sparks, John Spikes II, James Ting, Collin Weintraub, and María Daniela Orellana Zambrano.
For support and encouragement throughout the process, we are grateful to Thao Pham, Jinky Flang, and Jonathan
Kirsch, Esq. Thanks to Louise Petersen for organizing and supporting the project. Thanks to our publisher, McGraw
Hill, for the valuable assistance of its staff, including Bob Boehringer, Jeffrey Herzich, Christina Thomas, Kristian
Sanford, and Don Goyette.
We are also very grateful to Dr. Fred Howell and Dr. Robert Cannon of Textensor Ltd for providing us extensive
customization and support for their powerful Annotate.co collaborative editing platform (www.annotate.co), which
allows us to efficiently manage thousands of contributions. Thanks to Dr. Richard Usatine and Dr. Kristine Krafts
for their outstanding image contributions. Thanks also to Jean-Christophe Fournet (www.humpath.com), Dr. Ed
Uthman, and Dr. Frank Gaillard (www.radiopaedia.org) for generously allowing us to access some of their striking
photographs.
For exceptional editorial leadership, enormous thanks to Megan Chandler, Mauri Loemker, Julie Mangoff, and
Emma D. Underdown. Special thanks to our indexer, Dr. Anne Fifer. We are also grateful to our illustrators,
Susan Mazik, Artemisa Gogollari, and Marvin Bundo, for their creative work on the new and updated
illustrations. Lastly, tremendous thanks to GW Inc., especially Anne Banning, Victoria Brown, Gary Clark, Cindy
Geiss, and Denise Smith.
Louisville Tao Le
Boracay Vikas Bhushan
Goldsboro, NC Matthew Sochat
Kuwait Humood Boqambar
Iowa City Kristina Damisch
Philadelphia Connie Qiu
New York City Jordan Abrams
Atlanta Caroline Coleman
San Francisco Kimberly Kallianos

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xv
Each year we are fortunate to receive the input of thousands of medical students and graduates who provide new
material, clarifications, and potential corrections through our website and our collaborative editing platform.
This has been a tremendous help in clarifying difficult concepts, correcting errata from the previous edition, and
minimizing new errata during the revision of the current edition. This reflects our long-standing vision of a true,
student-to-student publication. We have done our best to thank each person individually below, but we recognize
that errors and omissions are likely. Therefore, we will post an updated list of acknowledgments at our website,
www.firstaidteam.com/bonus/. We will gladly make corrections if they are brought to our attention.
For submitting contributions and corrections, many thanks to Raed Ababneh, Nursultan Abdreyev, Youni Abdul,
Lana Abusalem, Bradley Acott, Temiloluwa Adejuyigbe, Gauri Adhikari, Ather Adnan, Rasim Agaev, Huzaifa
Ahmad, Rija Ahmad, Oluwabukola Ajagbe, Tongwa B. Aka, Nataly Kobra Akbarshahi, Shahad Aladnan, Amr
Alalwani, Nida Alam, Qutaiba Al-bustanji, Jose Alfonso, Maged Algazzar, Majed Alghamdi, Ahmed Al-Maidama,
Abdulmajeed Almehmadi, Feras Al-Moussally, Maria Alwan, Salman Alyahya, Hamza Amin, Chelsea Amo-
Tweneboah, Cara Anderson, Gina Andraos, Akanksha Reddy Annadi, Lordsfavour Anukam, Ali Arafa, Amalia
Ardeljan, Amalia Doris Ardeljan, Stephanie Asdell, Christopher Azzam, Wardah Bajwa, Brayton Ballenger,
Charlotte Banayan, Dileni C. Bandarage, Alyssa Barré, Isabella Batki, Jeffrey Baum, Tal Bavli, Jerrin Bawa, Alex
Belaia, Dimitri Benner, Alexandra Bennett, Ashley Best, Alexandros Bestavasvili, Rohan Bhan, Krish Bharat, Saeed
Bhuiyan, Pavit Bhullar, Jennifer Black, Lisle Blackbourn, William Bloom, Alina Bobrova, Luisa Brito, Chrys
Buckley, Olena Budarina, Jessica Budiselic, Eamonn Byrnes, Alfonso Caetta, Gabriela Maria Calderon, Santiago
Callegari, Sergio Camba, Xi Cao, Cristian Agapito Rosa Carrasquillo, Katie Carsky, Alicia Casella, Yasmin Chaiep,
Tina Chen, Santosh Cherian, Devina Chintaman, Akshit Chitkara, Maruf Chowdhury, Matthew J. Christensen,
Meaghan Clark, Courtney Cleveland, Aravind R. D., Yann Dacquay, Mohammed Dairywala, Jonathan Daou,
Aimen Asim Dar, Naveena Daram, Joe Demian, Andres Diaz, Amin Dice, Taurah Dizadare, Andreea Bianca
Dobre, Courtney Duckworth, Ismail Faruk Durmus, Manasa Dutta, Nikolas Echeverry, Matthew Eli, Awab
Elnaeem, Mohamed Kamal El-Naeim, Karim Eltaib, Holly Everett, Sarrah Fadul, Amin Farsani, Samia Fatima,
Yasmin Fazli, Kristina Flores, Farrar Ford, Katy Franks, Kyle Fratta, Shany Freund, Racha Ftouni, Ron Gadot, Don
Galinea-Faigao, Abhishek Gami, Henriette De La Garza, Daniel Gatazka, Nicolas Curi Gawlinski, Leo Georges,
Ashley Ghaemi, Paola Ghanem, Ahmad Munir Gharaibeh, Elie Ghasb, Brennan Gibson, Sam Gieg, Aastha Gohil,
Sanya Goswami, Sourabh Goyal, Jan Andre Grauman, Shreya Gulati, Avni Gupta, Nanditha Guruvaiah, Rossy
Guzman, Noon Hagmusa, Natalie Hassell, Christine Laura Heisen, Ghayda Hemadneh, Aryan Hemani, Trevor
Henderson, Briana Hernandez, Sarah Hossain, Sarahbeth Howes, Janie Hu, Vivian Hu, Jonathan Hunter, Lisa
Hysa, Ebuka Ibuoka, Mina Iskandar, Beck Jacobsen, Yamna Jadoon, Saira Jahangir, Ala Jamal, Tesmol James, Salem
Jaramne, Prayag Jariwala, Chloe Jensen, Hassan El Jesr, Bijay Jeswani, Ankit Juneja, Simrat Kahlon, Nabyl Kalaf,
Anastasia Kalantarova, Mohammed Kamareddine, Nivedita Kar, Arneet Kaur, Wajiha Kazmi, Azmeer Khamisani,
Ahmed Ali Khan, Jawad Khan, Sunil Babu Khanal, Bhumika Khanna, David S. Kim, Alex Kinzer, Anna Kislik,
Ramya Kommidi, Nicholas Koutrakis, Kushal Kriplani, Jonas Kruse, Mariia Kukushkina, Nimisha Kumar, Natalie
General Acknowledgments

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xvi
LaBossier, Nery y Mara Lamothe, Megan Lane, Joanna Lee, Victor Lee, Chime Lhatso, Xiantian Lin, Alwyn Louis,
Joshua St. Louise, Alexander Lu, Lisa-Qiao MacDonald, Divya Madhavarapu, Osama Magableh, Jalal Maghfour,
Reema Mahdi, Jainil Maheshwari, Rose Maisner, Freda Malanyaon, Mayra Malik, Mahir Mameledzija, Nikhil
Mankuzhy, Abdul Mannan, Yusra Mansour, Rebecca Irene Marshall, Bridget Martinez, Penelope Martinez, Shielah
Mauntana, O’Brian Mbakwe, Ashley McNeal, Bryan Medina, Mario Mekhail, Sherin Menachery, David Merkley,
Ibrahim El Mikati, Stephan A. Miller, Damir Mingaleev, Sarim Mirza, Niall James Moffett, Deena Mohamed,
Mahmoud Mohamed, Kompal Mohan, John Moon, Mohammad Murcy, Sakthi Murugan, Youjin Na, Geraldine
Nabeta, Rahul Nachnani, Shamsun Nahar, Zaid R. Kh Najdawi, Alice Nassar, Zachary Nelson, Judith Nnah,
Ahmed Noor, Ahmen Noor, Eric Nturibi, Anuli Nwankwo, Ahmad Obeidat, Ross O’Hagan, Cristal Osborne, Olga
Ostrovetsky, Ademola Osundeko, Majd Oteibi, Reinis Ozolins, Sophia Padelford, Andrew Palosaari, Zonghao Pan,
Niranjan Pandey, Mark Parker, Harshita Pasupuleti, Anmol Patel, Dharmik Patel, Krunal Patel, Manan Patel, Neha
Patel, Austin Patrick, Harry Paul, Dmytro Pavlenko, Matthew Pavlica, Dorian Perez, Samantha Perovski, Sahir
Pervaiz, Sofia Phirtskhalava, Mark Pilarski, Fanny Pimentel, Denise Powell, Shannon Powell, Meenu Prasad, Jacob
Proaño, Kevin Pruitt, Laith Rahabneh, Masum Rahman, Juhi Ramchandani, Lisnaldy Ramirez, Naresa Ramjohn,
Vaishnavi Rao, Adel Rasheed, Samyukta Ravi, Sreeram Ravi, Vishnu VB Reddy, Rafey Rehman, Jose Issac Reyes,
Kyle Robbins, Samuel Roberts, Quayd Robertson, Pedro Garcia Rodriguez, Helio Manuel Grullón Rodríguez,
Gessel Romero, Ariel Rucker, Angelica Maria Sanchez Ruiz, Megan Ryon, Bradley Ryva, Chantal Saberian,
George Saboura, Sumeet Saini, Allie Sakowicz, Vishad Samami, Jasneet Sandhu, Omar Sanduka, Prakriti Sapkota,
Dhruv Sarwal, Abeer Sarwar, M. Sathyanarayanan, Emma Schulte, Michael Schwarz, Justin Sedgewick, Jessica
Sefen, Neha Sehgal, Sirous Seifirad, Nicole Sequeira, Muhanad Shaib, Fahad Shaikh, Ahmed Shakir, Jeffrey
Shapiro, Muhammad Usman Sharif, Kanika Sharma, Manisha Sharma, Tina Sharma, Michelle Sheena, Emily
Sherry, Minghan Shi, Sami Shoura, Melanie Shpigel, Robert Shvarts, Naomi Siddiquee, Christina Siems, Anantha
Singarajah, Manik Inder Singh, Ramzi Y. Skaik, Bryn Smith, Emilie Song, Rishabh Soni, Luke Sorensen, Suganiya
Srikanthan, Abhinav Srinath, Hala M. Staitieh, Brett Stark, Hafsa Omer Sulaiman, Saranya Sundaram, Michael
Syrett, Nikolaos Syrigos, Basel Tamimi, Hamza Tariq, Aalap K. Trivedi, Amy Tsai, Athanasios Tsimpouras, Shannon
Tung, Akemini Udoro, Sheela Vaswani, Jasmine Vatani, Sandra Azareli Garcia Velázquez, Allen Wang, Shelly Wang,
Kaystin Weisenberger, Andrew White, Peter Williams, Stephanie Wottrich, Maria Yan, Hafsa Yaseen, Forrest Yeh,
Hsinyu Yin, Susan Yohannan, Jamie Yoon, Zurabi Zaalishvili, Syed Zeeshan Haider Zaidi, Caroline Zhao, Michael
Zheng, and Patrick Ziarnowski.

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xvii
This edition of First Aid for the USMLE Step 1 incorporates thousands of contributions and improvements suggested
by student and faculty advisors. We invite you to participate in this process. Please send us your suggestions for:
Study and test-taking strategies for the USMLE Step 1
New facts, mnemonics, diagrams, and clinical images
High-yield topics that may appear on future Step 1 exams
Personal ratings and comments on review books, question banks, apps, videos, and courses
For each new entry incorporated into the next edition, you will receive up to a $20 Amazon.com gift card as well as
personal acknowledgment in the next edition. Significant contributions will be compensated at the discretion of the
authors. Also, let us know about material in this edition that you feel is low yield and should be deleted.
All submissions including potential errata should ideally be supported with hyperlinks to a dynamically updated Web
resource such as UpToDate, AccessMedicine, and ClinicalKey.
We welcome potential errata on grammar and style if the change improves readability. Please note that First Aid style
is somewhat unique; for example, we have fully adopted the AMA Manual of Style recommendations on eponyms
(“We recommend that the possessive form be omitted in eponymous terms”) and on abbreviations (no periods with
eg, ie, etc). We also avoid periods in tables unless required for full sentences. Kindly refrain from submitting “style
errata” unless you find specific inconsistencies with the AMA Manual of Style or our diversity initiative as discussed
in the Foreword.
The preferred way to submit new entries, clarifications, mnemonics, or potential corrections with a valid,
authoritative reference is via our website: www.firstaidteam.com.
This website will be continuously updated with validated errata, new high-yield content, and a new online platform
to contribute suggestions, mnemonics, diagrams, clinical images, and potential errata.
Alternatively, you can email us at: firstaid@scholarrx.com.
Contributions submitted by May 15, 2021, receive priority consideration for the 2022 edition of First Aid for the
USMLE Step 1. We thank you for taking the time to share your experience and apologize in advance that we cannot
individually respond to all contributors as we receive thousands of contributions each year.
How to Contribute

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xviii
`` NOTE TO CONTRIBUTORS
All contributions become property of the authors and are subject to editing and reviewing. Please verify all data and
spellings carefully. Contributions should be supported by at least two high-quality references.
Check our website first to avoid duplicate submissions. In the event that similar or duplicate entries are received,
only the first complete entry received with valid, authoritative references will be credited. Please follow the style,
punctuation, and format of this edition as much as possible.
`` JOIN THE FIRST AID TEAM
The First Aid/ScholarRx team is pleased to offer paid editorial and coaching positions. We are looking for passionate,
experienced, and dedicated medical students and recent graduates. Participants will have an opportunity to work
on a wide variety of projects, including the popular First Aid series and the growing line of USMLE-Rx/ScholarRx
products, including Rx Bricks. Please use our webform at https://www.usmle-rx.com/join-the-first-aid-team/ to apply,
and include a CV and writing examples.
For 2021, we are actively seeking passionate medical students and graduates with a specific interest in improving our
medical illustrations, expanding our database of photographs (including clinical images depicting diverse skin types),
and developing the software that supports our crowdsourcing platform. We welcome people with prior experience
and talent in these areas. Relevant skills include clinical imaging, digital photography, digital asset management,
information design, medical illustration, graphic design, tutoring, and software development.

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xix
How to Use This Book
CONGRATULATIONS: You now possess the book that has guided nearly two million students to USMLE success
for over 30 years. With appropriate care, the binding should last the useful life of the book. Keep in mind that putting
excessive flattening pressure on any binding will accelerate its failure. If you purchased a book that you believe
is defective, please immediately return it to the place of purchase. If you encounter ongoing issues, you can also
contact Customer Service at our publisher, McGraw Hill.
START EARLY: Use this book as early as possible while learning the basic medical sciences. The first semester of
your first year is not too early! Devise a study plan by reading Section I: Guide to Efficient Exam Preparation, and
make an early decision on resources to use by checking Section IV: Top-Rated Review Resources. Note that First Aid
is neither a textbook nor a comprehensive review book, and it is not a panacea for inadequate preparation.
CONSIDER FIRST AID YOUR ANNOTATION HUB: Annotate material from other resources, such as class
notes or comprehensive textbooks, into your book. This will keep all the high-yield information you need in one
place. Other tips on keeping yourself organized:
For best results, use fine-tipped ballpoint pens (eg, BIC Pro+, Uni-Ball Jetstream Sports, Pilot Drawing Pen,
Zebra F-301). If you like gel pens, try Pentel Slicci, and for markers that dry almost immediately, consider
Staedtler Triplus Fineliner, Pilot Drawing Pen, and Sharpies.
Consider using pens with different colors of ink to indicate different sources of information (eg, blue for
USMLE-Rx Step 1 Qmax, green for UWorld Step 1 Qbank).
Choose highlighters that are bright and dry quickly to minimize smudging and bleeding through the page
(eg, Tombow Kei Coat, Sharpie Gel).
Many students de-spine their book and get it 3-hole-punched. This will allow you to insert materials from other
sources, including curricular materials.
INTEGRATE STUDY WITH CASES, FLASH CARDS, AND QUESTIONS: To broaden your learning strategy,
consider integrating your First Aid study with case-based reviews (eg, First Aid Cases for the USMLE Step 1), flash
cards (eg, USMLE-Rx Step 1 Flash Facts), and practice questions (eg, the USMLE-Rx Step 1 Qmax). Read the
chapter in the book, then test your comprehension by using cases, flash cards, and questions that cover the same
topics. Maintain access to more comprehensive resources (eg, ScholarRx Bricks and USMLE-Rx Step 1 Express
videos) for deeper review as needed.
PRIME YOUR MEMORY: Return to your annotated Sections II and III several days before taking the USMLE
Step 1. The book can serve as a useful way of retaining key associations and keeping high-yield facts fresh in your
memory just prior to the exam. The Rapid Review section includes high-yield topics to help guide your studying.
CONTRIBUTE TO FIRST AID: Reviewing the book immediately after your exam can help us improve the next
edition. Decide what was truly high and low yield and send us your comments. Feel free to send us scanned images
from your annotated First Aid book as additional support. Of course, always remember that all examinees are under
agreement with the NBME to not disclose the specific details of copyrighted test material.

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xx
Blood, Plasma, Serum Reference Range SI Reference Intervals
*Alanine aminotransferase (ALT, GPT at 30°C) 10–40 U/L 10–40 U/L
*Alkaline phosphatase 25–100 U/L 25–100 U/L
Amylase, serum 25–125 U/L 25–125 U/L
*Aspartate aminotransferase (AST, GOT at 30°C) 12–38 U/L 12–38 U/L
Bilirubin, serum (adult)
Total // Direct 0.1–1.0 mg/dL // 0.0–0.3 mg/dL 2–17 μmol/L // 0–5 μmol/L
*Calcium, serum (Total) 8.4–10.2 mg/dL 2.1–2.6 mmol/L
*Cholesterol, serum (Total) Rec: < 200 mg/dL < 5.2 mmol/L
*Creatinine, serum (Total) 0.6–1.2 mg/dL 53–106 μmol/L
*
Electrolytes, serum
Sodium (Na+
)
Chloride (Cl –
)
Potassium (K+
)
Bicarbonate (HCO3
–
)
Magnesium (Mg2+
)
136–146 mEq/L
95–105 mEq/L
3.5–5.0 mEq/L
22–28 mEq/L
1.5–2 mEq/L
136–146 mmol/L
95–105 mmol/L
3.5–5.0 mmol/L
22–28 mmol/L
0.75–1.0 mmol/L
Gases, arterial blood (room air)
P O 2
P CO 2
pH
75–105 mm Hg
33–45 mm Hg
7.35–7.45
10.0–14.0 kPa
4.4–5.9 kPa
[H+
] 36–44 nmol/L
*Glucose, serum Fasting: 70–100 mg/dL 3.8–6.1 mmol/L
Growth hormone − arginine stimulation Fasting: < 5 ng/mL
Provocative stimuli: > 7 ng/mL
< 5 μg/L
> 7 μg/L
Osmolality, serum 275–295 mOsmol/kg H2 O 275–295 mOsmol/kg H2 O
*Phosphorus (inorganic), serum 3.0–4.5 mg/dL 1.0–1.5 mmol/L
Prolactin, serum (hPRL) Male: < 17 ng/mL
Female: < 25 ng/mL
< 17 μg/L
< 25 μg/L
*Proteins, serum
Total (recumbent)
Albumin
Globulins
6.0–7.8 g/dL
3.5–5.5 g/dL
2.3–3.5 g/dL
60–78 g/L
35–55 g/L
23–35 g/L
Thyroid-stimulating hormone, serum or plasma 0.4–4.0 μU/mL 0.4–4.0 mIU/L
*Urea nitrogen, serum (BUN) 7–18 mg/dL 25–64 nmol/L
*Uric acid, serum 3.0–8.2 mg/dL 0.18–0.48 mmol/L
(continues)
Selected USMLE Laboratory Values
* = Included in the Biochemical Profile (SMA-12)

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xxi
Cerebrospinal Fluid Reference Range SI Reference Intervals
Cell count 0–5/mm3 0–5 × 10 6 /L
Glucose 40–70 mg/dL 2.2–3.9 mmol/L
Proteins, total < 40 mg/dL < 0.40 g/L
Hematologic
Erythrocyte count Male: 4.3–5.9 million/mm3
Female: 3.5–5.5 million/mm3
4.3–5.9 × 1012 /L
3.5–5.5 × 1012 /L
Erythrocyte sedimentation rate (Westergen) Male: 0–15 mm/hr
Female: 0–20 mm/hr
0–15 mm/hr
0–20 mm/hr
Hematocrit Male: 41–53%
Female: 36–46%
0.41–0.53
0.36–0.46
Hemoglobin, blood Male: 13.5–17.5 g/dL
Female: 12.0–16.0 g/dL
135–175 g/L
120–160 g/L
Hemoglobin, plasma < 4 mg/dL < 0.62 μmol/L
Leukocyte count and differential
Leukocyte count
Segmented neutrophils
Band forms
Eosinophils
Basophils
Lymphocytes
Monocytes
4,500–11,000/mm3
54–62%
3–5%
1–3%
0–0.75%
25–33%
3–7%
4.5–11.0 × 10 9
/L
0.54–0.62
0.03–0.05
0.01–0.03
0–0.0075
0.25–0.33
0.03–0.07
Mean corpuscular hemoglobin 25–35 pg/cell 0.39–0.54 fmol/cell
Mean corpuscular hemoglobin concentration 31%–36% Hb/cell 4.8–5.6 mmol Hb/L
Mean corpuscular volume 80–100 μm3 80–100 fL
Partial thromboplastin time (activated) 25–40 sec 25–40 sec
Platelet count 150,000–400,000/mm3 150–400 × 10 9
/L
Prothrombin time 11–15 sec 11–15 sec
Reticulocyte count 0.5–1.5% of RBCs 0.005–0.015
Urine
Creatinine clearance Male: 97–137 mL/min
Female: 88–128 mL/min
97–137 mL/min
88–128 mL/min
Osmolality 50–1200 mOsmol/kg H2 O 50–1200 mOsmol/kg H2 O
Proteins, total < 150 mg/24 hr < 0.15 g/24 hr
Other
Body mass index Adult: 19–25 kg/m 2 19–25 kg/m 2

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xxii
First Aid Checklist for the USMLE Step 1
This is an example of how you might use the information in Section I to prepare for the USMLE Step 1.
Refer to corresponding topics in Section I for more details.
Years Prior
Months Prior
Weeks Prior
One Week Prior
One Day Prior
Day of Exam
After Exam
Use top-rated review resources for first-year medical school courses.
Ask for advice from those who have recently taken the USMLE Step 1.
Review computer test format and registration information.
Register six months in advance.
Carefully verify name and address printed on scheduling permit. Make sure
the name on scheduling permit matches the name printed on your photo ID.
Be familiar with COVID-19 cancellation and rescheduling policies.
Go online for test date ASAP.
Define your exam goals (pass comfortably, beat the mean, ace the test)
Set up a realistic timeline for study. Cover less crammable subjects first.
Evaluate and choose study materials (review books, question banks).
Use a question bank to simulate the USMLE Step 1 to pinpoint strengths and
weaknesses in knowledge and test-taking skills.
Do test simulations in question banks.
Assess how close you are to your goal.
Pinpoint remaining weaknesses. Stay healthy (exercise, sleep).
Verify information on admission ticket (eg, location, date).
Remember comfort measures (loose clothing, earplugs, etc).
Work out test site logistics (eg, location, transportation, parking, lunch).
Print or download your Scheduling Permit and Scheduling Confirmation
to your phone.
Relax.
Lightly review short-term material if necessary. Skim high-yield facts.
Get a good night’s sleep.
Relax.
Eat breakfast.
Minimize bathroom breaks during exam by avoiding excessive morning
caffeine.
Celebrate, regardless of how well you feel you did.
Send feedback to us on our website at www.firstaidteam.com.
First Aid Checklist for the USMLE Step 1
This is an example of how you might use the information in Section I to prepare for the USMLE
Step 1. Refer to corresponding topics in Section I for more details.

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1
` Introduction 2
` USMLE Step 1—The
Basics 2
` Defining Your Goal 12
` Learning Strategies 13
` Timeline for Study 16
` Study Materials 20
` Test-Taking
Strategies 22
` Clinical Vignette
Strategies 23
` If You Think You
Failed 24
` Testing Agencies 25
` References 25
S E C T I O N I
Guide to Efficient
Exam Preparation
“One important key to success is self-confidence. An important key to self-
confidence is preparation.”
—Arthur Ashe
“Wisdom is not a product of schooling but of the lifelong attempt to
acquire it.”
—Albert Einstein
“Finally, from so little sleeping and so much reading, his brain dried up
and he went completely out of his mind.”
—Miguel de Cervantes Saavedra, Don Quixote
“Sometimes the questions are complicated and the answers are simple.”
—Dr. Seuss
“He who knows all the answers has not been asked all the questions.”
—Confucius
“The expert in anything was once a beginner.”
—Helen Hayes
“It always seems impossible until it’s done.”
—Nelson Mandela

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Guide to efficient exam PreParationSec tion i2
`` INTRODUCTION
Relax.
This section is intended to make your exam preparation easier, not harder.
Our goal is to reduce your level of anxiety and help you make the most
of your efforts by helping you understand more about the United States
Medical Licensing Examination, Step 1 (USMLE Step 1). As a medical
student, you are no doubt familiar with taking standardized examinations
and quickly absorbing large amounts of material. When you first confront
the USMLE Step 1, however, you may find it all too easy to become
sidetracked from your goal of studying with maximal effectiveness. Common
mistakes that students make when studying for Step 1 include the following:
Starting to study (including First Aid) too late
Starting to study intensely too early and burning out
Starting to prepare for boards before creating a knowledge foundation
Using inefficient or inappropriate study methods
Buying the wrong resources or buying too many resources
Buying only one publisher’s review series for all subjects
Not using practice examinations to maximum benefit
Not understanding how scoring is performed or what the score means
Not using review books along with your classes
Not analyzing and improving your test-taking strategies
Getting bogged down by reviewing difficult topics excessively
Studying material that is rarely tested on the USMLE Step 1
Failing to master certain high-yield subjects owing to overconfidence
Using First Aid as your sole study resource
Trying to prepare for it all alone
In this section, we offer advice to help you avoid these pitfalls and be more
productive in your studies.
`` USMLE STEP 1—THE BASICS
The USMLE Step 1 is the first of three examinations that you would
normally pass in order to become a licensed physician in the United
States. The USMLE is a joint endeavor of the National Board of Medical
Examiners (NBME) and the Federation of State Medical Boards (FSMB).
The USMLE serves as the single examination system domestically and
internationally for those seeking medical licensure in the United States.
The Step 1 exam includes test items that can be grouped by the organiza-
tional constructs outlined in Table 1 (in order of tested frequency). In late
2020, the NBME increased the number of items assessing communication
skills. While pharmacology is still tested, they are focusing on drug mecha-
nisms rather than on pharmacotherapy. You will generally not be required to
identify specific medications indicated for a specific condition. Instead, you
will be asked more about mechanisms and side effects.
` The test at a glance:
8-hour exam
Up to a total of 280 multiple choice items
7 test blocks (60 min/block)
Up to 40 test items per block
45 minutes of break time, plus another 15
if you skip the tutorial

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Guide to efficient exam PreParation Sec tion i 3
How Is the Computer-Based Test (CBT) Structured?
The CBT Step 1 exam consists of one “optional” tutorial/simulation block
and seven “real” question blocks of up to 40 questions per block with no
more than 280 questions in total, timed at 60 minutes per block. A short
11-question survey follows the last question block. The computer begins the
survey with a prompt to proceed to the next block of questions.
Once an examinee finishes a particular question block on the CBT, he or
she must click on a screen icon to continue to the next block. Examinees
cannot go back and change their answers to questions from any previously
completed block. However, changing answers is allowed within a block of
questions as long as the block has not been ended and if time permits.
What Is the CBT Like?
Given the unique environment of the CBT, it’s important that you become
familiar ahead of time with what your test-day conditions will be like. You
can access a 15-minute tutorial and practice blocks at http://orientation.
nbme.org/Launch/USMLE/STPF1. This tutorial interface is very similar to
the one you will use in the exam; learn it now and you can skip taking it
during the exam, giving you up to 15 extra minutes of break time. You can
gain experience with the CBT format by taking the 120 practice questions
(3 blocks with 40 questions each) available online or by signing up for a
practice session at a test center for a fee.
T A B L E 1 . Frequency of Various Constructs Tested on the USMLE Step 1.*
Competency Range, % System Range, %
Medical knowledge: applying foundational
science concepts
60–70 General principles 12–16
Patient care: diagnosis 20–25 Behavioral health & nervous systems/special senses 9–13
Communication and interpersonal skills 6–9 Respiratory & renal/urinary systems 9–13
Practice-based learning & improvement 4–6 Reproductive & endocrine systems 9–13
Discipline Range, % Blood & lymphoreticular/immune systems 7–11
Pathology 44–52 Multisystem processes & disorders 6–10
Physiology 25–35 Musculoskeletal, skin & subcutaneous tissue 6–10
Pharmacology 15–22 Cardiovascular system 5–9
Biochemistry & nutrition 14–24 Gastrointestinal system 5–9
Microbiology 10–15 Biostatistics & epidemiology/population health 4–6
Immunology 6–11 Social sciences: communication skills/ethics 6–9
Gross anatomy & embryology 11–15
Histology & cell biology 8–13
Behavioral sciences 8–15
Genetics 5–9
*Percentages are subject to change at any time. www.usmle.org

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Guide to efficient exam PreParationSec tion i4
For security reasons, examinees are not allowed to bring any personal
electronic equipment into the testing area. This includes both digital and
analog watches, cell phones, tablets, and calculators. Examinees are also
prohibited from carrying in their books, notes, pens/pencils, and scratch
paper. Food and beverages are also prohibited in the testing area. The
testing centers are monitored by audio and video surveillance equipment.
However, most testing centers allot each examinee a small locker outside
the testing area in which he or she can store snacks, beverages, and
personal items.
Questions are typically presented in multiple choice format, with 4–5
possible answer options. There is a countdown timer on the lower left corner
of the screen as well. There is also a button that allows the examinee to
mark a question for review. If a given question happens to be longer than
the screen (which occurs very rarely), a scroll bar will appear on the right,
allowing the examinee to see the rest of the question. Regardless of whether
the examinee clicks on an answer choice or leaves it blank, he or she must
click the “Next” button to advance to the next question.
The USMLE features a small number of media clips in the form of audio
and/or video. There may even be a question with a multimedia heart sound
simulation. In these questions, a digital image of a torso appears on the
screen, and the examinee directs a digital stethoscope to various auscultation
points to listen for heart and breath sounds. The USMLE orientation
materials include several practice questions in these formats. During the
exam tutorial, examinees are given an opportunity to ensure that both the
audio headphones and the volume are functioning properly. If you are
already familiar with the tutorial and planning on skipping it, first skip ahead
to the section where you can test your headphones. After you are sure the
headphones are working properly, proceed to the exam.
The examinee can call up a window displaying normal laboratory values.
In order to do so, he or she must click the “Lab” icon on the top part of
the screen. Afterward, the examinee will have the option to choose between
“Blood,” “Cerebrospinal,” “Hematologic,” or “Sweat and Urine.” The
normal values screen may obscure the question if it is expanded. The
examinee may have to scroll down to search for the needed lab values. You
might want to memorize some common lab values so you spend less time on
questions that require you to analyze these.
The CBT interface provides a running list of questions on the left part of the
screen at all times. The software also permits examinees to highlight or cross
out information by using their mouse. There is a “Notes” icon on the top
part of the screen that allows students to write notes to themselves for review
at a later time. Finally, the USMLE has recently added new functionality
including text magnification and reverse color (white text on black
background). Being familiar with these features can save time and may help
you better view and organize the information you need to answer a question.
` Keyboard shortcuts:
A, B, etc—letter choices
Esc—exit pop-up Calculator and Notes
windows
` Be sure to test your headphones during the
tutorial.
` Heart sounds are tested via media questions.
Make sure you know how different heart
diseases sound on auscultation.
` Illustrations on the test include:
Gross specimen photos
Histology slides
Medical imaging (eg, x-ray, CT, MRI)
Electron micrographs
Line drawings
` Familiarize yourself with the commonly
tested lab values (eg, Hb, WBC, platelets,
Na +
, K+
).

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Guide to efficient exam PreParation Sec tion i 5
For those who feel they might benefit, the USMLE offers an opportunity
to take a simulated test, or “CBT Practice Session” at a Prometric center.
Students are eligible to register for this three-and-one-half-hour practice
session after they have received their scheduling permit.
The same USMLE Step 1 sample test items (120 questions) available on
the USMLE website, www.usmle.org, are used at these sessions. No new
items will be presented. The practice session is available at a cost of $75
($155 if taken outside of the US and Canada) and is divided into a short
tutorial and three 1-hour blocks of ~40 test items each. Students receive a
printed percent-correct score after completing the session. No explanations
of questions are provided.
You may register for a practice session online at www.usmle.org. A separate
scheduling permit is issued for the practice session. Students should allow
two weeks for receipt of this permit.
How Do I Register to Take the Exam?
Prometric test centers offer Step 1 on a year-round basis, except for the
first two weeks in January and major holidays. The exam is given every day
except Sunday at most centers. Some schools administer the exam on their
own campuses. Check with the test center you want to use before making
your exam plans.
US students can apply to take Step 1 at the NBME website. This application
allows you to select one of 12 overlapping three-month blocks in which to be
tested (eg, April–May–June, June–July–August). Choose your three-month
eligibility period wisely. If you need to reschedule outside your initial three-
month period, you can request a one-time extension of eligibility for the next
contiguous three-month period, and pay a rescheduling fee. The application
also includes a photo ID form that must be certified by an official at your
medical school to verify your enrollment. After the NBME processes your
application, it will send you a scheduling permit.
The scheduling permit you receive from the NBME will contain your USMLE
identification number, the eligibility period in which you may take the exam,
and two additional numbers. The first of these is known as your “scheduling
number.” You must have this number in order to make your exam appointment
with Prometric. The second number is known as the “candidate identification
number,” or CIN. Examinees must enter their CINs at the Prometric
workstation in order to access their exams. However, you will not be allowed
to bring your permit into the exam and will be asked to copy your CIN onto
your scratch paper. Prometric has no access to the codes. Make sure to bring
a paper or electronic copy of your permit with you to the exam! Also bring
an unexpired, government-issued photo ID that includes your signature (such
as a driver’s license or passport). Make sure the name on your photo ID exactly
matches the name that appears on your scheduling permit.
` You can take a shortened CBT practice test at
a Prometric center.
` The Prometric website will display a calendar
with open test dates.

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Guide to efficient exam PreParationSec tion i6
Once you receive your scheduling permit, you may access the Prometric
website or call Prometric’s toll-free number to arrange a time to take the
exam. You may contact Prometric two weeks before the test date if you
want to confirm identification requirements. Be aware that your exam may
be canceled because of circumstances related to the COVID-19 pandemic
or other unforeseen events. If that were to happen, you should receive an
email from Prometric containing notice of the cancellation and instructions
on rescheduling. Visit www.prometric.com for updates regarding their
COVID-19 cancellation and rescheduling policies.
Although requests for taking the exam may be completed more than six months
before the test date, examinees will not receive their scheduling permits earlier
than six months before the eligibility period. The eligibility period is the three-
month period you have chosen to take the exam. Most medical students choose
the April–June or June–August period. Because exams are scheduled on a “first-
come, first-served” basis, it is recommended that you book an exam date on the
Prometric website as soon as you receive your permit. Prometric will provide
appointment confirmation on a print-out and by email. Be sure to read the
latest USMLE Bulletin of Information for further details.
What If I Need to Reschedule the Exam?
You can change your test date and/or center by contacting Prometric at
1-800-MED-EXAM (1-800-633-3926) or www.prometric.com. Make sure to
have your CIN when rescheduling. If you are rescheduling by phone, you must
speak with a Prometric representative; leaving a voicemail message will not
suffice. To avoid a rescheduling fee, you will need to request a change at least
31 calendar days before your appointment. Please note that your rescheduled
test date must fall within your assigned three-month eligibility period.
When Should I Register for the Exam?
You should plan to register as far in advance as possible ahead of your
desired test date (eg, six months), but, depending on your particular test
center, new dates and times may open closer to the date. Scheduling early
will guarantee that you will get either your test center of choice or one
within a 50-mile radius of your first choice. For most US medical students,
the desired testing window is in June, since most medical school curricula
for the second year end in May or June. Thus, US medical students should
plan to register before January in anticipation of a June test date. The timing
of the exam is more flexible for IMGs, as it is related only to when they
finish exam preparation. Talk with upperclassmen who have already taken
the test so you have real-life experience from students who went through a
similar curriculum, then formulate your own strategy.
Where Can I Take the Exam?
Your testing location is arranged with Prometric when you book your test
date (after you receive your scheduling permit). For a list of Prometric
locations nearest you, visit www.prometric.com.
` Be familiar with Prometric’s policies for
cancellation and rescheduling due to
COVID-19.
` Test scheduling is done on a “first-come,
first-served” basis. It’s important to schedule
an exam date as soon as you receive your
scheduling permit.
` Register six months in advance for seating
and scheduling preference.

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Guide to efficient exam PreParation Sec tion i 7
How Long Will I Have to Wait Before I Get My Scores?
The USMLE reports scores in three to four weeks, unless there are delays
in score processing. Examinees will be notified via email when their scores
are available. By following the online instructions, examinees will be able to
view, download, and print their score report online for ~120 days after score
notification, after which scores can only be obtained through requesting an
official USMLE transcript. Additional information about score timetables
and accessibility is available on the official USMLE website.
What About Time?
Time is of special interest on the CBT exam. Here’s a breakdown of the
exam schedule:
15 minutes Tutorial (skip if familiar with test format and features)
7 hours Seven 60-minute question blocks
45 minutes Break time (includes time for lunch)
The computer will keep track of how much time has elapsed on the exam.
However, the computer will show you only how much time you have
remaining in a given block. Therefore, it is up to you to determine if you
are pacing yourself properly (at a rate of approximately one question per 90
seconds).
The computer does not warn you if you are spending more than your
allotted time for a break. You should therefore budget your time so that
you can take a short break when you need one and have time to eat. You
must be especially careful not to spend too much time in between blocks
(you should keep track of how much time elapses from the time you finish a
block of questions to the time you start the next block). After you finish one
question block, you’ll need to click to proceed to the next block of questions.
If you do not click within 30 seconds, you will automatically be entered into
a break period.
Break time for the day is 45 minutes, but you are not required to use all of
it, nor are you required to use any of it. You can gain extra break time (but
not extra time for the question blocks) by skipping the tutorial or by finishing
a block ahead of the allotted time. Any time remaining on the clock when
you finish a block gets added to your remaining break time. Once a new
question block has been started, you may not take a break until you have
reached the end of that block. If you do so, this will be recorded as an
“unauthorized break” and will be reported on your final score report.
Finally, be aware that it may take a few minutes of your break time to “check
out” of the secure resting room and then “check in” again to resume testing,
so plan accordingly. The “check-in” process may include fingerprints,
pocket checks, and metal detector scanning. Some students recommend
pocketless clothing on exam day to streamline the process.
` Gain extra break time by skipping the
tutorial, or utilize the tutorial time to add
personal notes to your scratch paper.
` Be careful to watch the clock on your break
time.

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United States Medical Licensing Examination

First Aid for the USMLE Step 1 (2021)

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First Aid for the USMLE Step 1 2020, 30th Edition (2020)