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Step 1 Sample Test Answers + Explanations 2026
USMLE STEP 1 Free 120 Explanations
Updated Feb 2025
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Updated as of Feb 2025
Here are the detailed explanations of the new Free 120 NBME STEP 1 Sample Test Questions so you don’t waste your time trying to find the correct answers and explanations. We had our expert USMLE tutors who scored 260+ on their exams refine these answers and explanations for you so you can spend your valuable time learning!
You can download the Free 120 STEP 1 Sample Test Questions on the USMLE website here. The order of answers and explanations here is based on the online NBME platform (not the pdf) as of February 2025.
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Table of Contents
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Block 1
Question 1:
The correct answer is A. This 12-year-old patient has Slipped Capital Femoral Epiphysis (SCFE), as indicated by subacute pain, limping, and restricted range of motion, particularly in abduction, flexion, and internal rotation. These findings, combined with the patient’s obesity (BMI of 31), align with the classic risk factors for SCFE. For USMLE, a 12-14-year-old obese boy with hip pain, is usually due to SCFE.
Incorrect answers:
B. A family history of diabetes may increase the risk of developing diabetes, while osteoporosis is generally not hereditary, making it unlikely that this family history plays a role in SCFE
C. Albuterol is known to cause side effects such as hypokalemia and tremors. Inhaled budesonide is primarily associated with an increased risk of oral candidiasis, but neither medication is linked to SCFE.
D. Previous fractures can lead to malunion and deformities. Fractures within the joint are associated with an increased risk of early-onset osteoarthritis, but this is not relevant to SCFE.
E. Recent physical activity is more likely to cause muscle strain or bone pain from overuse, rather than SCFE. In this case, the symptoms began prior to the physical activity, ruling it out as a primary cause.
Question 2:
The correct answer is D. This patient has Keratosis Pilaris (KP), given the chronic (>3 months) history of a non-itchy, non-painful rash. The photograph likely shows the lateral arm with multiple erythematous papules. These lesions are typical of KP, which occurs without edema, pustules, or excoriations.
Incorrect answers:
A. Eczema (atopic dermatitis) is typically pruritic and characterized by the presence of excoriations due to scratching. It commonly affects flexor surfaces, such as the elbows and knees. The absence of itching and excoriations in this patient makes eczema an unlikely diagnosis.
B. Folliculitis often presents as pustules surrounding hair follicles. This patient’s rash lacks pustules, inflammation, or pain, ruling out folliculitis.
C. Hidradenitis suppurativa (HS) presents as painful skin lesions in intertriginous areas (e.g., axillae, inguinal region). It is characterized by abscesses, adhesions, and sinus tract formation, none of which are present in this patient.
F. Urticaria consists of pruritic wheals with well-defined borders that coalesce into patches. Urticaria typically resolves within hours
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Question 3:
The correct answer is B. This patient has obstructive sleep apnea (OSA) as evidenced by daytime somnolence. The patient also has features of obesity hypoventilation syndrome (OHS), including severe obesity (BMI of 63), cyanosis, and abnormal arterial blood gas findings indicating respiratory acidosis (pH 7.31, high PCO2 of 70, and low PO2). Chronic hypoxia stimulates hypoxia-inducible factor 2 (HIF-2), which increases erythropoietin production and results in elevated hemoglobin and red blood cell mass. OSA patients may present with Hypertension (due to hypoxia), Depression or Atrial fibrillation (due to HTN, Atrial enlargement).
Incorrect answers:
A. In respiratory acidosis, the proper metabolic compensation is metabolic alkalosis, not acidosis. This patient’s bicarbonate would be elevated, not decreased.
C. Obesity causes extrinsic restrictive lung disease, which reduces total lung capacity (TLC). Therefore, TLC should be decreased, not increased.
D. Chronic hypoxia can lead to generalized pulmonary vasoconstriction, causing pulmonary hypertension, which increases pressure in the right ventricle and leads to right ventricular hypertrophy. The left ventricle is not typically affected in this scenario.
Question 4:
The correct answer is A. This patient most likely has Goodpasture syndrome (anti-glomerular basement membrane antibody disease), evidenced by the presence of pulmonary symptoms (hemoptysis, diffuse bilateral crackles, low oxygen saturation) and renal symptoms (dark urine, dysmorphic RBCs, RBC casts, elevated creatinine). The linear deposition of IgG supports the diagnosis of Goodpasture syndrome. Goodpasture syndrome is an autoimmune disorder forming antibodies against collagen which classically affects the lungs and the kidneys as in this patient. The presence of crescent formation indicates rapidly progressive glomerulonephritis (RPGN) that denotes a worse prognosis
Incorrect answers:
B. Anti-double-stranded DNA antibodies are specific to SLE. Although nephritic syndrome can occur, the presence of linear IgG deposition and concurrent pulmonary and renal symptoms suggests another diagnosis.
C. Nucleolar protein antibodies (Anti Smith) are associated with SLE, which is not supported by the findings in this case.
D. Antiphospholipid antibody syndrome is primarily a thrombotic disorder and does not present with linear IgG deposition or crescentic glomerulonephritis.
E. ANCA-associated vasculitides cause pauci-immune RPGN, which lacks immune deposits on immunofluorescence, unlike the linear IgG deposition seen here.
Question 5:
The correct answer is D. This patient has a Horseshoe kidney, evidenced by the ultrasonic finding and history of recurrent UTIs. It occurs due to the fusion of the inferior poles of the metanephros during embryological development, leading to abnormal kidney positioning. Horseshoe kidney is a common finding with Turner syndrome. It increases the risk of UTIs.
Incorrect answers:
A. While kidney ascension and rotation are important for normal kidney development; they do not contribute to the formation of horseshoe kidney
B. Similarly, to option A, ascension and rotation are essential for normal kidney development, but they are not responsible for the fusion seen in horseshoe kidney.
C. Failure of the ureteric bud to develop results in agenesis or absence of the kidney, not horseshoe kidney. The ureteric bud plays a key role in kidney development through inductive signaling.
Question 6:
The correct answer is E. This patient is recently treated for mycobacterium with ciprofloxacin and rifampin. Doubling the dose of warfarin would typically result in a higher INR value; however, the metabolism of warfarin has been accelerated due to rifampin inducing the P450 system, leading to decreased plasma concentrations and subtherapeutic INR levels. Medications that inhibit P450 system: Cimetidine, Ciprofloxacin, Omeprazole, Ketoconazole, Erythromycin, Protease Inhibitors and Grapefruits. (COKE, PIe and Grapefruits)
Incorrect answers:
A. Decreased protein binding would result in an increased free concentration of warfarin, leading to a supratherapeutic INR (increased bleeding time).
B. Eradication of gut flora reduces vitamin K synthesis, which would lead to an increased INR, not a subtherapeutic level as seen in this patient.
C. The patient’s alcohol intake remains stable (two 12-oz beers daily), making it unlikely to contribute to the current findings.
D. Increased consumption of vitamin K-rich vegetables (e.g., spinach) can decrease warfarin efficacy and result in subtherapeutic INR levels; however, this would typically affect baseline INR values and not require doubling the warfarin dose as seen in this patient.
Question 7:
The correct answer is C. This patient presents with a 2-week history of fever, throat pain, bilateral tonsillar exudate, and generalized lymphadenopathy, which are consistent with mononucleosis-like symptoms. The negative heterophile antibody test rules out Epstein-Barr virus infection (Choice A). Given the presence of anemia, thrombocytopenia, and leukopenia, HIV is the most likely diagnosis. For USMLE, mononucleosis-like symptoms, suspect EBV, CMV, Toxoplasmosis and HIV.
Incorrect answers:
A. Epstein-Barr virus infection is ruled out by the negative heterophile antibody (Monospot) test.
B. Gonococcal pharyngitis is associated with fever, tonsillar exudate, and localized lymphadenitis, but it does not typically cause generalized lymphadenopathy or the laboratory abnormalities seen in this patient.
D. Lymphogranuloma venereum infection is usually associated with a painless genital ulcer and painful inguinal lymphadenopathy, not the generalized lymphadenopathy or throat symptoms seen here.
E. Streptococcal pharyngitis typically presents with fever, sore throat with exudates, and localized cervical lymphadenopathy. It is an acute infection, unlike this patient’s subacute presentation.
Question 8:
The correct answer is A. This patient has poorly controlled hypertension, evidenced by the high blood pressure of 180/105, headache, and shortness of breath. Ophthalmoscopic examination typically shows arteriovenous nicking due to the compression of the artery when it crosses over the vein, which is a classic sign of severe uncontrolled hypertension. Other findings include flame-shaped hemorrhages, and cotton-wool spots.
Incorrect answers:
B. Melanocytes in the uvea are unlikely to be associated with a history of hypertension. These are more commonly associated with abundant skin moles or melanocytic lesions and not hypertension.
C. Optic neuritis typically presents with visual changes and pain, often seen in conditions like multiple sclerosis, rather than hypertension.
D. Posterior subcapsular cataracts are associated with gradual vision loss, glare, and halos around light but are not linked with high blood pressure
E. Tractional retinal detachment is usually attributed to diabetic retinopathy and presents with gradual vision loss, which is not characteristic of the hypertensive changes seen in this patient.
Question 9:
The correct answer is D. This patient has neurological deficits that include the inability to speak (motor aphasia), weakness of the right lower side of the face, and difficulty swallowing. In the context of atrial fibrillation on the ECG and neurological deficits, an embolic stroke to the left middle cerebral artery (MCA) is most likely. The MCA supplies Broca’s area, which is crucial for speech production. The patient’s history of rheumatic mitral valve disease is a known risk factor for the development of atrial fibrillation and subsequent embolic stroke.
Incorrect answers:
A. The anterior inferior cerebellar artery (AICA) supplies the lateral pons, which gives:
Ipsilateral facial paralysis (lower motor neuron type), Loss of taste from anterior two-thirds of tongue (CN VII), Ipsilateral loss of pain and temperature from face (spinal trigeminal nucleus & tract), Contralateral loss of pain and temperature from body (spinothalamic tract), Ipsilateral hearing loss & tinnitus (cochlear nucleus, labyrinthine artery involvement), Vertigo, nausea, vomiting, nystagmus (vestibular nuclei), Ipsilateral limb ataxia (middle cerebellar peduncle), and Horner syndrome (sympathetic tract)
B. The superior cerebellar artery supplies the upper part of the cerebellum and is typically associated with cerebellar symptoms like ataxia. A stroke here would not produce symptoms like aphasia or weakness seen in this patient
C. The posterior cerebral artery supplies the occipital cortex, and a stroke in this artery would cause contralateral homonymous hemianopia, typically with macular sparing
E. The anterior communicating artery connects the anterior cerebral arteries and is involved in strokes that impede blood flow to the medial cerebral cortex. This can lead to lower extremity weakness and personality changes, but it would not cause the speech deficits seen in this patient.
Question 10:
The correct answer is A. This patient has a history of GERD, and he reports that the omeprazole becomes ineffective around the holidays. It’s crucial to explore how much he is eating and drinking during this time, as overeating can increase intragastric pressure, worsening reflux symptoms. Alcohol consumption could also result in drug interactions and relaxation of the lower esophageal sphincter, further exacerbating symptoms. Chronic GERD is associated with Metaplasia of the lower esophagus(Barrett esophagus) which can lead to Esophageal adenocarcinoma.
Incorrect answers:
B. Although it’s important to prevent the progression of Barrett esophagus, the patient feels well except during the holidays. The primary concern here is the temporary worsening of symptoms due to overeating and alcohol consumption
C. Ordering an upper endoscopy may not be the best next step. First, taking more detailed information from the patient about his eating and drinking habits will help identify the cause of the medication’s ineffectiveness.
D. Referral to a gastroenterologist may be considered if conventional anti-reflux medications don’t work. But first the physician should rule out the common causes of ineffectiveness making this the unlikely answer.
E. Switching to pantoprazole or another medication could be an option if symptoms persist despite lifestyle modifications, but it’s not the first action to take.
Question 11:
The correct answer is C. This patient has manifestations of pernicious anemia due to vitamin B12 deficiency, which is supported by the neurological findings (weakness, tingling in the hands and feet, irritability, forgetfulness, hyperreflexia, spasticity), megaloblastic anemia, antiparietal cell antibodies, and elevated serum methylmalonic acid and total homocysteine. The neurological symptoms are consistent with subacute combined degeneration (SCD), affecting both the dorsal columns and lateral corticospinal tract of the spinal cord. Vitamin B12 is essential for DNA synthesis and the maturation of red blood cells. Deficiency impairs division of RBCs and accumulation of homocysteine and decreased methionine formation.
Incorrect answers:
A. A vitamin B6 deficiency, not B12, would lead to decreased conversion of homocysteine to cysteine, and would be associated with sideroblastic anemia.
B. Glutamine is typically accumulated in cases of hepatic encephalopathy, presenting with delirium and altered mental status.
D & E. Phenylalanine and Tyrosine are important for neurotransmitter synthesis, but its abnormality is not associated with blood cell abnormalities.
Question 12:
The correct answer is B. This patient has new metastatic lesions in the liver and lungs. Metastatic spread from the right side of the colon follows this pathway: the superior mesenteric vein drains blood from the right colon into the portal vein, which then enters the liver. From the liver, cancer cells can spread through the hepatic veins, into the inferior vena cava (IVC), and subsequently to the heart (right atrium and right ventricle) and pulmonary vasculature, leading to metastasis in the lungs.
Incorrect answers:
A & C. These veins drain the left side of the colon, NOT the right
D. The middle colic artery supplies part of the transverse colon and does not contribute to venous drainage or cancer spread.
E. The pulmonary veins carry oxygenated blood from the lungs to the left atrium and are not involved in the metastatic process.
F. Arteries do not play a primary role in the venous spread of metastases.
G. The superior vena cava drains blood from the upper body (head, neck, and upper extremities) and does not play a role in this metastatic process.
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Question 13:
The correct answer is F. This patient presents with a 1-week history of increased urination and excessive thirst, along with a low urine osmolality that corrects after administration of desmopressin (an ADH analogue). These findings are consistent with central diabetes insipidus (DI), which is caused by decreased production of ADH. The supraoptic nucleus of the hypothalamus is responsible for synthesizing ADH (vasopressin). Vasopressin test is used to differentiate between Central vs nephrogenic DI.
Incorrect answers:
A. The anterior pituitary gland secretes hormones such as GH, prolactin, ACTH, TSH, FSH, and LH. Dysfunction here typically presents with signs like fatigue, failure to lactate.
B. Damage to Bowman space this structure would result in glomerular diseases, such as glomerulonephritis, characterized by proteinuria, hematuria, and renal dysfunction, which are not present here.
C. Damage to the glomerulus, as seen in glomerulonephritis, leads to proteinuria, hematuria, and renal impairment. This patient does not have such findings.
D. The hypophysial portal system is a network of blood vessels connecting the hypothalamus to the anterior pituitary and is not involved in ADH production or release.
E. The loop of Henle is primarily involved in concentrating urine via the Na/K/2Cl co-transporter. Genetic abnormalities of this channel can cause Bartter syndrome, which mimics the effects of loop diuretics. However, Bartter syndrome would not respond to ADH administration.
Question 14:
The correct answer is C. This patient’s intermittent headache is likely a symptom of poorly controlled hypertension (154/100 mmHg). The ECG findings of tall R waves in leads V5-V6 and left axis deviation are indicative of left ventricular hypertrophy (LVH). LVH develops as an adaptive response to chronic hypertension, where there is increased synthesis of contractile filaments (actin and myosin) within existing myocytes, leading to myocyte hypertrophy rather than hyperplasia. In chronic HTN, sarcomeres are added in parallel.
Incorrect answers:
A. Excessive accumulation of glycogen is characteristic of glycogen storage diseases such as Pompe disease, which typically causes cardiomyopathy or systemic symptoms unrelated to the hypertrophic changes seen in this patient.
B. Fibrosis of intraventricular conduction pathways can lead to conduction abnormalities and arrhythmias. However, the occasional skipped beats described in this patient are more consistent with benign premature atrial contractions (PACs) and do not explain the LVH.
D. Misfolding and aggregation of cytoskeletal proteins result in dilated cardiomyopathy (DCM), not LVH. DCM is characterized by ventricular dilation and systolic dysfunction, which are not evident in this patient.
E. Myocyte hyperplasia refers to an increase in the number of myocytes, which is not a mechanism for hypertrophy. In LVH, the adaptive response involves increased actin and myosin synthesis within existing myocytes rather than cell proliferation.
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Question 15:
The correct answer is B. This patient has manifestations suggestive of exocrine pancreatic insufficiency, including steatorrhea (fatty stools), significant weight loss, and a dry, scaly rash. These symptoms are consistent with fat malabsorption and subsequent deficiency of fat-soluble vitamins, such as vitamin A. Pancreatic insufficiency leads to decreased secretion of digestive enzymes (e.g., lipase), impairing the absorption of fats and fat-soluble vitamins. Vitamin A deficiency commonly manifests as xerosis (dry skin). Stool testing is a good test to screen for malabsorption due to pancreatitis.
Incorrect answers:
A. Magnesium deficiency typically presents with symptoms such as muscle cramps, fatigue, and, in severe cases, arrhythmias and neuromuscular excitability.
C. Vitamin B12 deficiency results in megaloblastic anemia and neurological symptoms, including loss of proprioception, ataxia, and weakness.
D. Vitamin C is water-soluble, and its deficiency causes scurvy, characterized by bleeding gums, perifollicular hemorrhages, and impaired wound healing.
E. Zinc deficiency can cause dermatitis, especially around body orifices (mouth, anus), impaired wound healing, anosmia, and hypogonadism in men. The dry scaly rash in this patient is more consistent with vitamin A deficiency rather than zinc deficiency.
Question 16:
The correct answer is B. The 95% confidence interval (CI) is calculated using the formula: CI=Xˉ±(Z×SE)
Where:
- Xˉ=130, Z=1.96, SE=5.0
- Calculation:
CI=130± (1.96×5)
CI=130± (9.8)
Range:
Lower limit: 130−9.8=120.2 mg/dL130 – 9.8 = 120.2
130−9.8=120.2mg/dL
- Upper limit: 130+9.8=139.8 mg/dL130 + 9.8 = 139.8
130+9.8=139.8mg/dL
Thus, the 95% CI for the true population mean is 120.2–139.8 mg/dL
Question 17:
The correct answer is E. This patient’s pulmonary function test shows an obstructive pattern (decreased FEV1: FVC ratio, increased residual volume). Additionally, the chest X-ray reveals hyperinflation and hyperlucency in the lower lobes of the lung. These findings, along with the barrel chest and pursed-lip breathing, are classic for emphysema. DLCO can differentiate between Emphysema(Decreased) and Chronic bronchitis(Normal) in COPD patients.
Incorrect answers:
A. Asthma is usually associated with wheezing, cough, and difficulty breathing. The chest X-ray is typically normal between attacks. The presence of barrel chest and pursed lips supports another diagnosis.
B. Bronchiectasis is characterized by chronic foul-smelling sputum, which may occasionally contain blood. Patients often have recurrent episodes of infection requiring antibiotic use. The obstructive pattern seen here is unlikely to be caused by bronchiectasis.
C. Chronic pulmonary fibrosis presents with a restrictive pattern (normal or increased FEV1: FVC ratio). Chest X-ray typically shows a reticulonodular pattern, not hyperinflation or hyperlucency.
D. Cystic fibrosis usually manifests at a younger age. Imaging often shows dilated bronchi (bronchiectasis), which is not consistent with this patient’s presentation.
Question 18:
The correct answer is D. A Type II error (also known as a β error) occurs when the null hypothesis is not rejected, even though it is actually false. In other words, it happens when a true effect is present, but the study fails to detect it. By increasing the sample size, the statistical power(1-B) of the study is improved, which means the study is more likely to correctly detect a real effect if it exists. This increase in power(1-B) reduces the probability of making a Type II error (β error). Increasing Sample size leads to increased power while decreasing alpha error leads to increased confidence level.
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Question 19:
The correct answer is B. This patient presents with clinical manifestations (indigestion, abdominal bloating, early satiety) and biopsy findings suggestive of gastric adenocarcinoma. The loss of epithelial cadherins (such as E-cadherin) is a key molecular event in cancer metastasis. These cadherins are responsible for maintaining cell-cell adhesion. For tumor to metastasize: Loss of E-Cadherins> increase Collagenase activity> spread via lymph node or blood.
Incorrect answers:
A. Cathepsin D is a lysosomal protease that is involved in protein degradation.
C. Heparin-binding fibroblast growth factors are involved in angiogenesis and tissue repair.
D. Integrins play a role in cell adhesion to the extracellular matrix and in signal transduction. They are not typically downregulated in gastric cancer, and their decreased expression is not as directly involved in the process of metastasis as the loss of cadherins.
E. Type IV collagenase is involved in the degradation of the basement membrane during tumor invasion. It is typically upregulated in many cancers.
F. Vascular endothelial growth factor (VEGF) is a key molecule in angiogenesis, and its expression is often increased in cancers to promote tumor growth and metastasis.
Question 20:
The correct answer is D. This patient has features of insulin resistance (elevated fasting glucose and BMI), which is common in metabolic syndrome and prediabetes. As a result, her body compensates by producing more insulin to overcome the resistance in tissues like adipose and muscle. Therefore, her insulin levels are likely to be elevated. In early DM, insulin level is high to overcome high glucose. Later, Pancreas gets exhausted and low insulin levels ensue.
Incorrect answers:
A. Insulin resistance and metabolic syndrome are generally associated with increased cholesterol production and altered lipid profiles, NOT decreased cholesterol excretion. Elevated insulin levels promote lipid storage and increase hepatic lipogenesis.
B. Increased adipose tissue, especially in postmenopausal women, contributes to the conversion of androstenedione to estrone.
C. Leptin, a hormone secreted by adipocytes, plays a role in regulating energy balance and satiety. In obesity and increased adiposity, leptin levels are typically increased.
E. Increased growth hormone levels are typically associated with acromegaly, a condition characterized by abnormal growth of bones and soft tissues, leading to enlarged hands, feet, and facial features.
F. Elevated TSH levels are indicative of primary hypothyroidism, which can lead to weight gain. However, this patient’s weight gain is more likely related to insulin resistance and metabolic syndrome rather than thyroid dysfunction.
Question 21:
The correct answer is C. The points on the same curve represent the same contractility, meaning they correspond to the appropriate end-diastolic volume for a given cardiac output. The slope of the curve represents contractility, so any transition along the same curve (e.g., W to Y) occurs with unchanged contractility. This patient presents with findings suggestive of an acute STEMI in the anterolateral leads (ST-segment elevation in V4 to V6, new Q waves, and increased serum troponin I). In anterolateral STEMI, the left ventricular function is compromised due to reduced blood supply, leading to decreased contractility. The resulting decreased contractility reduces stroke volume, which decreases cardiac output and increases end-diastolic volume (blood left in the ventricle due to impaired ejection).
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Question 22:
The correct answer is A. This patient has manic symptoms with psychotic features as described in this scenario. Manic symptoms include rapid speech, loose associations, and lack of sleep. Psychotic features include hallucinations (hearing voices) and delusions (married to the president’s twin brother, receiving instructions from a higher being). it’s differentiated from Schizoaffective disorder as the latter is characterized by psychotic symptoms at least 2 weeks with the absence of Mood disorder.
Incorrect answers:
B. Brief psychotic disorder involves psychotic symptoms lasting less than 30 days. This patient’s symptoms have persisted for more than 2 months, in addition to manic episodes, ruling out this diagnosis.
C. Delusional disorder is characterized by fixed, false beliefs, but the patient usually functions well otherwise. This patient displays marked impairment and manic features, which exclude this diagnosis.
D. Psychotic disorder due to a general medical condition requires evidence of an underlying medical condition causing the symptoms. No information in this scenario supports such a diagnosis.
E. Schizophrenia requires symptoms (e.g., hallucinations, delusions, disorganized speech) to persist for >6 months. Additionally, the presence of manic symptoms strongly supports a different diagnosis.
Question 23:
The correct answer is D. While delivering bad news, the physician should wait until the parents are emotionally ready to disclose the full information. The most critical part is delivering the diagnosis of Down syndrome, a common genetic condition, in a clear and empathetic manner.
Incorrect answers:
A. While the primary care physician may later provide additional details or ongoing support, the consulting physician has the responsibility to disclose as much information as is immediately relevant.
B. Allowing time to tell other family members is not the reason for initially withholding additional details. The approach is focused on the parents’ emotional readiness, not external communication.
C. Parental distress is an inevitable reaction to such news. The goal is not to delay distress but to manage it effectively by prioritizing clarity and emotional support.
E. Decisions about medically appropriate actions can be discussed after the initial diagnosis and emotional processing have occurred. The focus at this stage is on delivering the diagnosis itself.
Question 24:
The correct answer is B. This patient most likely has benign prostatic hyperplasia (BPH) as suggested by the chronic history of urinary hesitancy, dribbling after urination, and an enlarged, firm prostate on digital rectal examination. Growth of prostatic glands is mediated by dihydrotestosterone, which is synthesized from testosterone by the enzyme 5α-reductase. DHT is important for growth of external genitalia and prostate. Testosterone is important for growth of internal genitalia except Prostate.
Incorrect answers:
A. Activation of the α1-adrenergic receptor causes vasoconstriction, leading to increased vascular resistance and hypertension, but it does not contribute to prostatic hyperplasia.
C. Conversion of testosterone to estradiol does not contribute to prostatic growth. In fact, estradiol is associated with effects like reducing prostatic size and is not directly involved in the pathogenesis of BPH.
D. Inhibition of the α1-adrenergic receptor relaxes the smooth muscle of the prostate and bladder neck, relieving obstructive symptoms.
E. Prostate-specific antigen (PSA) is used as a marker for prostate disorders. While PSA levels can be elevated in BPH or prostatic adenocarcinoma, its production does not directly cause BPH.
Question 25:
The correct answer is B. This patient most likely has a pneumothorax due to the knife wound to the chest. Tachycardia and tachypnea are common in this condition. A large pneumothorax can shift the mediastinum to the opposite side. On physical examination, you would find decreased tactile fremitus, hyperresonance on percussion (due to the presence of air), and decreased breath sounds because the lung is unable to expand properly.
Incorrect answers:
A. A dull percussion sound is more typical of conditions like pleural effusion, not pneumothorax, which causes hyperresonance due to air in the pleural space.
C. The presence of dull percussion and decreased breath sounds does not align with pneumothorax findings.
D. Bronchial breath sounds are usually heard in areas of consolidation, not over a pneumothorax.
E. Increased fremitus and dull percussion are not expected with a pneumothorax.
Question 26:
The correct answer is D. This patient most likely has MEN2A syndrome, which is suggested by the presence of pheochromocytoma and a neck mass likely originating from parafollicular cells, most likely thyroid carcinoma. Additionally, the family history of the disease further supports the diagnosis. MEN2A is associated with mutations in the RET proto-oncogene. MEN2A is associated Thyroid carcinoma, Parathyroid hyperplasia, Pheochromocytoma (TPP)
Incorrect answers:
A. Cell cycle regulation genes include TP53, RB, Cyclins, CDKs. RET oncogene is unrelated.
B. DNA mismatch repair genes include MLH1, MSH2. They are involved in Hereditary non polyposis colorectal cancers. RET oncogene is unrelated.
C. Metastasis suppressor genes generally inhibit spread of tumors. RET oncogene in unrelated.
E. Tumor suppressor genes include TP53, RB. RET oncogene is unrelated.
Question 27:
The correct answer is C. This patient most likely has a dissecting aortic aneurysm involving the left carotid artery and distal aortic arch. The classic symptoms of severe upper neck pain and a history of hypertension are suggestive of this condition. The presence of Horner syndrome (ptosis, miosis, anhidrosis) indicates involvement of the sympathetic plexus around the carotid artery. Right-sided hemiplegia is due to disruption of blood flow to the left cerebral cortex via the left carotid artery. The decreased left radial pulse is caused by interruption of blood flow to the left subclavian artery. Dissection causes manifestations depending on the artery it involves.
Incorrect answers:
A. Dissection of the descending aorta typically leads to low blood pressure and decreased pulses in the lower extremities, which doesn’t explain the right-sided hemiplegia seen in this patient.
B. Dissection of the left carotid artery may cause hemiplegia and ptosis, but it wouldn’t explain the decreased left radial pulse, which suggests involvement of the subclavian artery.
D. Dissection of the proximal aorta extending into the right subclavian artery could lead to cardiac issues like acute myocardial infarction or cardiac tamponade but doesn’t explain right-sided hemiplegia or the decreased left radial pulse.
E. A superior sulcus tumor (Pancoast tumor) is associated with Horner syndrome but typically affects the intrinsic hand muscles, which is not observed in this case.
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Question 28:
The correct answer is E. This patient most likely has transitional cell carcinoma (TCC) of the renal pelvis, also known as urothelial carcinoma. Risk factors for this condition include smoking and occupational exposure to naphthylamine. The presentation fits with the typical features of TCC, including hematuria and possible associated symptoms. For USMLE, removed organs most likely indicate a malignant tumor or non-viable tissues. For example, in case of oncocytoma, the kidney is unlikely to be removed.
Incorrect answers:
A. Angiomyolipoma is associated with tuberous sclerosis, but there are no other features of this syndrome present in this case.
B. Melanoma would typically present with a pigmented lesion, often on the skin, and its risk factors include sun exposure and fair skin. This patient’s symptoms do not fit the presentation of melanoma.
C. Nephroblastoma (Wilms tumor) is most commonly seen in children, especially between the ages of 2 and 4. It is unlikely to present in an adult patient.
D. Oncocytomas are benign renal masses usually discovered incidentally during imaging for other conditions. They do not present with symptoms like those seen in this case.
Question 29:
The correct answer is B. This patient’s findings, including shortness of breath, tachycardia, tachypnea, and deep vein thrombosis (DVT) in the right calf, are consistent with a pulmonary embolism (PE). Risk factors such as long flights and a predisposition to thrombosis (due to genetic factors or medications) are significant. Factor V Leiden mutation is associated with an inability to break down factor V, which leads to thrombosis. Factor V Leiden mutation is the most common cause of hereditary thrombophilia. Suspect it in any case of atypical thrombosis, such as cavernous sinus thrombosis or hepatic vein thrombosis.
Incorrect answers:
A. While antithrombin III deficiency increases the risk of thrombosis, it is usually asymptomatic and far less common than Factor V Leiden. Additionally, higher doses of heparin are needed to produce an effect in patients with antithrombin III deficiency.
C. Hemophilia would result in bleeding, not thrombosis, and is not associated with the clinical presentation described.
D. Protein C deficiency is much less common than Factor V Leiden and would also be associated with a higher risk of thrombosis, but it is not the most likely cause in this case. Usually it occurs in the first few days of warfarin use but this patient has no such history of drug use.
E. Von Willebrand disease is a bleeding disorder and would not cause thrombosis.
Question 30:
The correct answer is D. This patient has symptomatic syringomyelia, as evidenced by the gradual progression of upper extremity weakness and decreased pain sensation. MRI confirms the diagnosis by showing a central syrinx in the cervical spine. A history of trauma increases the risk of syrinx formation. Fine touch and vibratory sense are spared in syringomyelia, except in advanced disease.
Incorrect answers:
A. A strict vegan diet may lead to vitamin B12 deficiency. vitamin B12 deficiency causes subacute combined degeneration which can present as sensory, motor and balance deficits that are distributed all over the body not only limited to the upper extremities.
B. A family history could increase the risk of certain conditions like Rheumatoid arthritis and osteoarthritis.
C. Recent travel increases the risk of deep vein thrombosis (DVT), which typically presents with unilateral leg swelling, pain, and erythema rather than the neurological deficits seen in this patient.
E. Unintended weight loss is commonly associated with malignancies. This patient’s history and MRI findings suggest post-traumatic syringomyelia rather than a neoplastic process.
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Question 31:
The correct answer is D. This 3-year-old boy most likely has rhabdomyosarcoma, given the presence of a bulging eye without a history of trauma. Biopsy confirms the diagnosis by identifying striations within muscle cells. Immunohistochemistry can demonstrate expression of desmin
Incorrect answers:
A. Neuroblastoma typically presents as an abdominal mass that may cross the midline and is associated with catecholamine secretion (e.g., hypertension, sweating). While it can metastasize to the orbit, it would usually be accompanied by systemic symptoms such as weight loss or irritability.
B. Pheochromocytoma is a catecholamine-secreting tumor of the adrenal medulla, presenting with episodic hypertension, headaches, palpitations, and tremors. It is rare in children and does not cause unilateral eye bulging.
C. Retinoblastoma presents with leukocoria (white pupillary reflex) rather than proptosis. It is a malignancy of the retina and is not associated with muscle striations on biopsy.
E. Thyroid cancer typically presents as a painless midline neck mass
Question 32:
The correct answer is E. This patient with sickle cell disease (SCD) likely has gallstones due to chronic hemolysis, which increases unconjugated bilirubin levels. When bilirubin levels exceed the bile’s solubility capacity, bilirubin stones form a common complication of chronic hemolytic anemias, including SCD. in SCD, patients with functional asplenia are at higher risk for infections against encapsulated organisms. and complications like gallstones.
Incorrect answers:
B. Decreased bile salt reabsorption occurs in malabsorption syndromes (e.g., Crohn’s disease, ileal resection), leading to cholesterol stone formation due to impaired micelle formation, but this is not the mechanism in SCD.
C. Increased cholesterol-to-bile ratio is common in cholesterol stone formation, typically seen in middle-aged, obese, fertile women due to estrogen’s effect on cholesterol metabolism. This does not explain gallstones in an SCD patient.
A & D. These options do not contribute significantly to gallstone formation in this patient’s case.
Question 33:
The correct answer is D. In a normal distribution, 68% of values fall within ±1 SD, 95% within ±2 SD, and 99.7% within ±3 SD of the mean. The mean leukocyte count is 7500, and the distribution is normal, meaning that 50% of values are above and 50% are below the mean. Make sure you remember The 68, 95 and 99.7 Rule.
Incorrect answers:
A. This represents the values that fall between -2 SD and +2 SD, which includes 95% of the population.
B. This represents values that are lower than -1 SD (16%) and higher than +1 SD (16%), Sum values are 32%.
C. This represents the values that fall between -1 SD and +1 SD, which includes approximately 68% of observations.
E. This represents the values above +2 SD, which account for only 2.5% of the population
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Question 34:
The correct answer is A. This patient most likely has Sarcoidosis, which presents with symptoms like fatigue, constipation, and frequent urination, as well as hypercalcemia (calcium level of 11.1 mg/dL). Sarcoidosis is characterized by bilateral hilar lymphadenopathy and interstitial lung infiltrates on chest x-ray. The hypercalcemia is most commonly due to increased calcitriol production by activated macrophages within the granulomas. For USMLE, the common presentation of sarcoidosis is a middle aged African American woman with cough and bilateral hilar adenopathy on CXR.
Incorrect answers:
B. While local cytokine release due to tumor metastases can lead to hypercalcemia, the patient’s clinical presentation, including chest x-ray findings, is more consistent with Sarcoidosis
C. Parathyroid hormone-related peptide (PTHrP) secretion typically occurs in paraneoplastic syndromes, such as in squamous cell carcinoma of the lung. This would present with a solitary lung mass, which is not seen here.
D. Increased secretion of parathyroid hormone is typically associated with hyperparathyroidism and could lead to hypercalcemia. However, this patient’s decreased parathyroid hormone levels suggest a different cause of hypercalcemia.
E. Hyperthyroidism can sometimes cause hypercalcemia, but in this patient, there are no classic symptoms of hyperthyroidism (such as weight loss, heat intolerance, or tachycardia), making this an unlikely cause of the hypercalcemia.
Question 35:
The correct answer is A. This patient most likely has Candida vaginitis, given her symptoms of vaginal pain, itching, and white discharge. Her history of diabetes increases the risk of fungal infections. The photomicrograph showing pseudohyphae and branching further supports the diagnosis. The treatment includes topical fluconazole. it grows within the normal pH of vagina.
Incorrect answers:
B. Chlamydia typically causes cervicitis rather than vaginitis, and its discharge is not characteristically white. Diagnosis is usually confirmed with NAAT
C. Herpes simplex virus type 2 (HSV-2) usually presents with painful ulcers and vesicles rather than white vaginal discharge. It is diagnosed PCR or viral culture.
D. Human papillomavirus (HPV) can lead to cervical squamous cell carcinoma, which may cause bleeding and ulceration. However, this patient’s symptoms are more consistent with an infection rather than a malignancy.
E. Trichomonas vaginalis infection typically presents with a green, frothy discharge rather than white discharge. A wet mount preparation would show motile trichomonads, which are not described in this case.
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Question 36:
The correct answer is C. This patient has a spinal cord injury at the T1 level, as indicated by the weakness and atrophy of the intrinsic hand muscles and loss of sensation below the clavicles (which corresponds to the T1 dermatome). The hyperreflexia and increased muscle tone in the lower extremities suggest involvement of the corticospinal tract, a hallmark of upper motor neuron dysfunction. The C5-T1 spinal segments innervate the upper extremity. The lower the spinal level, the more distal the motor function impairment.
Incorrect answers:
A & B. A lesion at C5 (choice A) or C7 (choice B) would likely affect the biceps (C5) or triceps (C7) reflexes, but in this patient, both reflexes are normal, ruling out these levels.
D & E. A lesion at T3 (choice D) or T5 (choice E) would spare the hand muscles, since these levels do not contribute to the brachial plexus. Sensory loss at these levels would also follow the corresponding intercostal dermatomes rather than starting at the clavicles.
Question 37:
The correct answer is D. This patient most likely has familial hypercholesterolemia supported by the presence of tendinous xanthomas, high cholesterol (410 mg/dl), and early-onset myocardial infarction. Family history also supports the diagnosis. LDL receptor deficiency leads to decreased clearance of LDL cholesterol, resulting in hypercholesterolemia. Medications targeted to decrease LDL receptor recycling can help treat this condition.
Incorrect answers:
A. Apo B48 is associated with abetalipoproteinemia, which is diagnosed in infancy. It’s characterized by the presence of steatorrhea and deficiency of fat-soluble vitamins. Lab value shows low VLDL, LDL, chylomicrons and cholesterol
B & E. Deficiency of Apo C and LPL activity are associated with hypertriglyceridemia and pancreatitis, not hypercholesterolemia.
C. Reduced HMG-CoA reductase activity is associated with low levels of cholesterol. Statins work by inhibiting this enzyme to lower cholesterol, which contradicts the findings in this patient.
Question 38:
The correct answer is E. This patient most likely has a stretched aortic annulus. The clinical presentation of severe, sharp upper back pain, along with hemodynamic instability (hypotension and tachycardia), is characteristic of aortic dissection. The presence of a diastolic murmur over the left sternal border suggests aortic valve regurgitation, which can occur due to dissection of the aortic root. When the dissection extends into the aortic annulus, it causes dilatation of the aortic root, which leads to incompetence of the aortic valve. This results in aortic regurgitation. The patient’s tall stature is a key feature of Marfan syndrome, which is often associated with aortic root dilation and increased risk for aortic dissection.
Incorrect answers:
A. Atrial septal defect typically presents with a wide, fixed splitting of the second heart sound and is not associated with acute hemodynamic collapse or diastolic murmurs.
B. Mitral stenosis is characterized by an opening snap and a diastolic murmur at the apex, which does not match this patient’s murmur location or presentation.
C. Papillary muscle rupture is a complication of myocardial infarction and leads to acute mitral regurgitation, causing a holosystolic murmur at the apex rather than a diastolic murmur.
D. Perforated tricuspid valve is typically associated with infective endocarditis, particularly in intravenous drug users, and presents with a systolic murmur rather than a diastolic murmur.
Question 39:
The correct answer is B. This patient likely has damage to the left medial longitudinal fasciculus (MLF), which connects the oculomotor and abducens nerves to coordinate horizontal eye movements. The MLF transmits signals from the abducens nucleus to the contralateral oculomotor nucleus. Damage to the left MLF prevents the left oculomotor nerve from synchronizing with the right abducens nerve, resulting in impaired eye movement, especially during rightward gaze. This causes the left eye to fail to adduct, a hallmark of internuclear ophthalmoplegia (INO), which is often associated with multiple sclerosis (MS).
Incorrect answers:
A. A left abducens nerve (CN VI) lesion would cause impaired abduction of the left eye.
C. A lesion of the left abducens nucleus would result in ipsilateral horizontal gaze palsy due to affection of the left abducens nerve and the right MLF connecting the left abducens and right oculomotor nerve.
D. A right abducens nerve (CN VI) lesion would cause impaired abduction of the right eye
E. A lesion of the right MLF would cause impaired adduction of the right eye on leftward gaze, which does not match this patient’s findings.
F. A lesion of the right abducens nucleus would result in ipsilateral horizontal gaze palsy due to affection of the right abducens nerve and the left MLF connecting the right abducens and left oculomotor nerve.
Question 40:
The correct answer is D. Type II pneumocytes are the most likely cells to proliferate and repair the alveolar epithelial layer in a patient recovering from acute respiratory distress syndrome (ARDS). These cells play a crucial role in surfactant production.
Incorrect answers:
A. Endothelial cells line blood vessels and facilitate gas exchange but do not play a role in repairing the alveolar epithelium.
B. Red blood cells are responsible for oxygen transport and do not participate in alveolar epithelial repair.
C. Type I pneumocytes facilitate gas exchange and are the majority of the alveolar epithelium. However, they do not proliferate to repair the alveolar epithelium.
E. Alveolar macrophages are responsible for the phagocytosis of inhaled pathogens but are not involved in the repair of the alveolar epithelium.
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