The Complete Step 2 CK Breakdown by Subject and How to Plan For Each Subject

Just like other USMLE exams, Step 2 CK is written based on a content outline and has a subject breakdown. Medicine makes up 50-60% of the exam, surgery is 25-30%, pediatrics is 20-25%, obstetrics and gynecology is 10-20%, and psychiatry is 10-15%. The test is further broken down into 15 major categories, which are made up of general principles or individual organ systems. This article will focus on the subject breakdown of USMLE Step 2 CK and how to plan your studying for each topic. High-yield test topics within each category will be highlighted. Keep in mind that Step 2 will likely include some topics beyond what is discussed here, so the more you study and know, the better prepared you will be. With that said, this is a good place to start your studies for each category. Your UWorld question bank will be your main study resource. You can use this article to create a study outline and/or identify your weaker topics for review.

You can see the updated list of Step 2 CK subjects on the USMLE website here.

General Principles of Foundational Science (2-4%)

The USMLE website describes this category saying that it “includes normal and abnormal processes that are not limited to specific organ systems.” Due to the generality of this category, it is hard to plan what exactly to study for it. This category may include some Step 1 material, such as drug mechanisms. However, considering this only makes up a very minor part of the test, it is best to focus on studying for other topics rather than reviewing Step 1 material. It is likely that you will come across the material in this category simply by reviewing other categories.

Immune System (3-5%)

There are a number of high-yield topics within this subject of Step 2 CK. Make sure to review the roles of different types of immune cells, including the activation and maturation of B and T cells, and the pathologies that can result from any immune deficiencies. Know the four types of hypersensitivity reactions – the physiology and examples of each. Included in this category are also types of grafts and types of rejection in regard to transplanted organs. Finally, amongst one of the high-yield topics in this category are vaccines. Know the differences between primary and secondary immune responses and passive vs active immunity. Though lower yield, this category may also include mechanisms of actions and side effects of immunosuppressive medications.

Blood & Lymphoreticular System (4-6%)

For this Step 2 CK subject from our breakdown, make sure you review the components of whole blood, blood types, Ph status, and transfusion reactions. You should also be able to interpret labs, including complete blood count with differential (CBC) and coagulation studies. Though the test does provide normal ranges for all of these, it is useful to memorize the common normal numbers, such as WBC, RBC, hemoglobin, platelets, etc. This will allow you to move through the questions quicker and reduce test day anxiety. In terms of pathology, you will need to study different types of anemia, sickle cell, thalassemia, and various vitamin deficiencies, such as folate and B12. Make sure you know the pathophysiology of each and what blood smear findings you can expect to find. You should be able to draw out the coagulation cascade and know the pathologies that result from various efficiencies in coagulation. Commonly used drugs that affect clotting should also be reviewed, including warfarin, heparin, aspirin, thrombin inhibitors, etc. As for the lymphoreticular system, know the differences amongst various types of leukemias and lymphomas. The questions for these often give patient presentations, so know the signs and symptoms of each.

Behavioral Health (6-8%)

This is usually the most straightforward topic on Step 2 CK and often one that does not require extensive studying in comparison to some of the other subjects in this breakdown. You should know the DSM-5 criteria for major physiological disorders, such as depression, anxiety, and bipolar. The most difficult part about this section is often the details on psychiatric drugs. The mechanisms and side effects of these are heavily tested. 

Nervous System & Special Senses (6-8%)

This category is basically a neurology shelf exam. Some of the important high-yield topics included in this section are stroke presentations, workup, and management. You should review different types of seizures and medications for these. The findings in different types of dementia are highly tested. Be able to do the workup and differentiate the causes of vertigo. The presentation, pathophysiology, and treatment of diseases of the nervous system will often appear on the test. These include ALS, MG, Lambert-Eaton, Guillain-Barre, and MS. Finally, you should know the common causes of back pain as well as rare causes. Especially, be able to identify AAA as an emergency (since this often presents with back pain), though this is not a neurologic disease. 

Musculoskeletal System / Skin & Subcutaneous Tissue (6-10%)

As you may have already observed on your shelf exams, the features, workup, and treatment of different skin cancers, especially melanoma, are heavily tested. Be able to differentiate these lesions in photos, including the different types of melanomas. Benign skin lesions should also be reviewed, as well as various high-yield rashes – dermatologic, and those that can indicate a pathology in another organ, such as the necrolytic migratory erythema in glucagonoma. As for the musculoskeletal system, you should review common dislocations and fractures and what nerves or blood vessels can be affected – these questions appear a lot. Pathologies of the hand such as carpal tunnel and trigger finger tend to show up. Finally, soft tissue sarcomas and other soft tissue masses, though rare, are commonly tested. 

Cardiovascular System (8-10%)

The cardiovascular system is amongst the top tested topics on Step 2 CK, and an important subject to the breakdown of the exam. In particular, Step 2 likes to test normal and pathologic physiology. Make sure you understand the anatomy and normal functions of the heart. This is usually best reviewed in videos, like OnlineMedEd. Make sure you understand the Frank-Starling curve and be able to apply it. In terms of cardiac pathology, know how congestive heart failure and atherosclerosis develop. Be able to identify common arrhythmias through both, a description of what they look like and by looking at an EKG. You should also know coronary artery disease, ischemic heart disease, and acute coronary syndromes. Given that the cardiovascular system makes up to 10% of the test, it is reasonable to allot more time for reviewing it.

Respiratory System (7-9%)

For the respiratory system, one of the highest-yield topics is lung cancer, including the workup of a lung nodule, screening guidelines, and the differences between the types of lung cancer. Make sure that you know which types of cancer are common in which populations and whether the nodules are commonly centrally or peripherally located. Another common topic is pleural effusions – memorize the Lights criteria and be able to apply it. Diffuse parenchymal lung diseases, though rarely seen on the wards, can appear on Step 2, so review the pathophysiology of each. You should understand the Virchow’s triad, Wells’ Criteria, and the causes and physiology of pulmonary embolisms. Other topics to review include asthma, COPD, and ARDS.

Gastrointestinal System (7-9%)

The GI system is extensive and includes many medical and surgical diseases. It will be important to know when surgical treatment is appropriate. Common surgically treated diseases include those of the gallbladder (acute cholecystitis, cholangitis, etc.), esophageal disorders, perforated peptic ulcers, and various cancers, starting from the esophagus and ending in the rectum. Make sure to review esophageal and colon cancers, as these are amongst the most heavily tested. As for the medical part of the GI system, you should review commonly tested workups – diarrhea (acute and chronic), jaundice, dysphagia, malabsorption, and GI bleeding. As you may know, the differences/similarities between Crohn’s and UC are high-yield Step 2 CK subjects, as well as the differences between different types of hepatitis and their serologies. 

Renal & Urinary System & Male Reproductive (4-6%)

Renal is one of those systems, like cardiac, where normal anatomy and physiology are commonly tested on Step 2 CK. Make sure you review different parts of the nephron and understand its function. Electrolyte imbalances are included in this section, so you should know the common causes and treatments of hypo/hypernatremia, hypo/hyperkalemia, hypo/hypercalcemia (association with parathyroid is important here), as well as acid-base disturbances. Be able to differentiate amongst the causes of AKI and be familiar with stages of CKD. For the urinary system, review common pediatric embryologic pathologies, such as posterior urethral valves and hypospadias. Finally, know the common presentations of renal, bladder, prostate, and testicular cancers and the treatments for each. 

Pregnancy, Childbirth & the Puerperium (4-6%)

Normal physiologic changes in pregnancy are important to understand and differentiate from pathological causes of these changes. Commonly tested pathologies are ectopic pregnancy, different types of abortions, preeclampsia and eclampsia, postpartum hemorrhage, and perinatal infections (helpful to memorize these with the TORCH mnemonic, but you should also know those not included in this mnemonic). You should know common forms of birth control and their effectiveness as well as the normal screenings during pregnancy. Normal stages of labor and the evaluations performed during labor as well as pre and post-term complications or pregnancy are also highly tested on Step 2 CK. You should know the basics of how a C-section is performed as well as when it is indicated.

Female Reproductive System & Breast (4-6%)

This is the gynecology section of Step 2 CK in the subject breakdown. Make sure to review the normal female pelvic and breast anatomy. You should know how to evaluate and manage adnexal masses, vaginal bleeding, abnormal uterine bleeding, and primary/secondary amenorrhea. Risks, workup, and treatment of cervical, endometrial, ovarian, and vaginal cancers are heavily tested, high-yield Step 2 CK content. The pathophysiology and features of PCOS overlap with other organ systems and are important to review. Breast is mainly a surgical topic. You should be familiar with common benign breast masses and their treatment. Breast cancer screening, workup, and treatment will most likely show up on the test. 

Endocrine System (4-6%)

Though this is not the biggest section on Step 2 CK, you can gain easy points here if you understand the hormonal pathways and commonly tested concepts. Draw out and understand the HP axis, as well as the pathways of other hormones secreted by the anterior and posterior pituitary. Make sure you understand how negative feedback works in these pathways and the pathologies that result if it malfunctions. You should review the workup of a thyroid nodule, hyperthyroidism/hypoparathyroidism, and thyroid cancers’ key characteristics (such as orphan Annie eyes nuclei for a papillary carcinoma). Understand the different types of hyperparathyroidism – primary, secondary, and tertiary. Though rare in clinical practice, MEN syndromes are very commonly tested – draw out a table for these. You should also know the presentation of pancreatic neuroendocrine tumors, whether each of these are benign or malignant, and which hormone is involved. Review common pathologies of both pituitaries and the adrenal glands. Endocrine also includes diabetes and its complications, such as DKA, so be sure to review this heavily tested topic.

Multisystem Processes & Disorders (4-6%)

This is another topic within Step 2 CK that is difficult to predict in terms of test content and their part in the exam breakdown. For this, think of diseases that can affect multiple organ systems, but do not dedicate your time studying for this particular category. You will come across the material contained in this category by reviewing all the organ systems.

Biostatistics & Epidemiology / Population Health / Interpretation of Medical Literature

There are a few high-yield Step 2 CK topics within this category. Biostatistics is often easy to learn, but also easy to forget if it has been a minute since you had to apply this knowledge. It is best to review this section early in your studies, and then again towards the end. It may also be helpful to make a one-page sheet with important formulas that you can look over the morning of your test day. This page should include the tables for sensitivity/specificity, PPV/NPV, and formulas for relative risk, odds ratio, types of errors and their significance for the null hypothesis, and the p-value curve. For population health, you should know different types of prevention, general vaccine schedules, and high-yield screening guidelines (who, when, and how), such as colon/lung/cervical/breast cancers, AAA, HIV, smokers. You should know the different types of clinical trials, the phases of a clinical trial, and how to interpret results in a study using the power and p-values. 

Social Sciences: Legal / Ethical Issues & Professionalism / Systems – based Practice and Patient Safety

This section is very straightforward in the Step 2 CK topic breakdown. You have seen these questions on the MCAT and on Step 1. The best way to prepare for this is simply doing practice questions.

If you noticed, there is no pediatrics included in the categories. This is because the pediatric diseases are included within the organ systems, so make sure to review these. Important topics to review for pediatrics are neonatal care and various neonatal pathologies and their workup (failure to pass meconium, emesis, jaundice, congenital defects). You should be able to recognize infectious rashes and common pathologies of the ears, nose, and throat given the presentations and sometimes images. Embryologic pathologies such as atrial and venous septal defects, and VACTERL abnormalities often appear. Be able to identify when child abuse has occurred and know the next steps. 

USMLE Step 2 is a comprehensive test. You can think of it as a combination of all the topics from your NBME shelf exams, so it is important that you study a lot for these, as it will set you up for success on the USMLE. Focus your studying on the categories that make up most of the test, particularly the organ systems. Good luck!

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