TheoryUSMLE Step 3 Medical Prep Practice Questions
Free USMLE Step 3 Medical Prep practice questions with answers and plain-English explanations. Browse the PDF, video and online mock test.
USMLE Step 3 Medical Prep Questions
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Q1A 15-month-old boy is brought to the office for a well-child visit. His mother reports that he does not yet speak any words and does not respond when she calls his name. He can pull to stand and cruise along furniture but does not walk independently. Physical examination shows normal growth parameters. He makes limited eye contact and does not wave bye-bye. The physician reviews standardized developmental screening results indicating delays in both language and social domains. Which of the following screening timelines and actions is most appropriate for this patient? Age Screening Type Action if Delay Identified Key Red Flags 9 months General developmental Refer to early intervention (Part C) No babbling, poor social engagement 18 months General + autism-specific Immediate referral to early intervention + audiology No single words, no pointing, no imitation 24 months Autism-specific Immediate referral for autism evaluation No two-word phrases, loss of skills 30 months General developmental Refer to early intervention if not improving Persistent language or motor delays
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✓ Correct answer: Immediate referral to early intervention and audiology evaluation
This 15-month-old has significant red flags: no single words by 15 months (expected by 12 months), limited social engagement, and not responding to name. These findings warrant immediate referral to early intervention (IDEA Part C) and audiology evaluation to rule out hearing loss. Distractor1 delays necessary intervention. Distractor2 is premature for autism-specific screening before 18 months. Distractor3 inappropriately delays action. Distractor4 misses the need for audiology assessment when language delay is present.
Q2A 7-month-old girl is brought to the office for evaluation. Her parents report that she has not yet started babbling and rarely smiles at them. She can sit with support but cannot sit independently. She reaches for toys with a raking grasp. Birth history is unremarkable and she was born at 39 weeks' gestation. Physical examination shows normal growth parameters. She makes inconsistent eye contact and does not turn toward sounds. Hearing screening at birth was normal. Which of the following milestone patterns is most concerning and warrants urgent evaluation?
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✓ Correct answer: Absent babbling and poor social smile at 7 months
Red flags warranting urgent evaluation include no social smile by 2 months and no babbling by 9 months. At 7 months, absent babbling combined with poor social engagement (rarely smiles, inconsistent eye contact) represents significant delay in multiple domains requiring immediate assessment. Distractor1 describes normal development (sitting independently expected 6-9 months). Distractor2 reflects normal fine motor development (raking grasp appropriate for age). Distractor3 is less concerning as independent walking develops 9-15 months. Distractor4 describes normal variation in language timeline.
Q3A 4-year-old boy with acute lymphoblastic leukemia in remission is brought to the office for a well-child visit. His mother reports that he missed multiple vaccinations during chemotherapy treatment, which ended 6 months ago. His current medications include daily mercaptopurine. Laboratory studies show absolute neutrophil count 1800/mm³ and absolute lymphocyte count 1200/mm³. According to his immunization record, he has not received MMR, varicella, or DTaP vaccines since age 12 months. His oncologist confirms he is no longer severely immunocompromised. Which of the following vaccination schedules is most appropriate? Vaccine Type Minimum Age Minimum Interval Contraindication in Immunocompromise MMR Live 12 months 28 days from other live vaccine Severe immunocompromise Varicella Live 12 months 28 days from other live vaccine Severe immunocompromise DTaP Inactivated 6 weeks 4 weeks between doses None IPV Inactivated 6 weeks 4 weeks between doses None
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✓ Correct answer: Administer DTaP today, then MMR and varicella together in 4 weeks
Inactivated vaccines (DTaP) can be given immediately. Live vaccines (MMR, varicella) require waiting at least 3 months after severe immunosuppression ends; at 6 months post-chemotherapy, he is eligible. Live vaccines must be spaced 28 days apart if not given concurrently, so MMR and varicella should be administered together. Distractor1 violates the 28-day spacing rule for sequential live vaccines. Distractor2 incorrectly continues contraindication beyond necessary timeframe. Distractor3 inappropriately delays inactivated vaccine. Distractor4 violates live vaccine spacing requirements.
Q4A 9-month-old boy is brought to the office for evaluation of poor weight gain. His mother reports he has been irritable during feedings and often refuses to eat. Review of his growth chart shows serial measurements as follows: Age Weight Weight Percentile Length Length Percentile 2 months 5.8 kg 75th 58 cm 50th 4 months 6.9 kg 50th 63 cm 50th 6 months 7.2 kg 25th 66 cm 50th 9 months 7.5 kg 5th 69 cm 25th
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✓ Correct answer: Crossing two major percentile lines from 75th to 5th over 7 months
Concerning growth pattern is crossing two major percentile lines (75th to 5th) over a short interval, indicating failure to thrive. Weight deceleration is disproportionate to length, suggesting inadequate caloric intake rather than genetic short stature. This requires comprehensive evaluation including feeding history, psychosocial assessment, and laboratory studies. Distractor1 describes normal proportional growth. Distractor2 represents constitutional growth variant. Distractor3 shows stable percentiles. Distractor4 misinterprets the data pattern.
Q5A 16-year-old girl comes to the office for a routine health maintenance examination. Her mother accompanies her and remains in the room. The patient appears healthy and reports no concerns. After completing the physical examination, the physician asks the mother to step out to speak with the patient privately. Once alone, the patient reports that she has been sexually active with her boyfriend for 3 months and wants to start oral contraceptives. She says her mood has been 'okay' but admits to feeling 'stressed' about school. She denies suicidal thoughts, substance use, or concerns about her relationship. Which of the following is the most appropriate next step?
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✓ Correct answer: Perform confidential screening for depression and risky behaviors, then discuss contraception
Adolescent visits require confidential screening for depression, sexual behavior, and substance use per HEEADSSS assessment guidelines. The patient's request for contraception and report of stress warrant depression screening before prescribing. State laws generally allow minors to consent for reproductive health services. Distractor1 violates confidentiality and adolescent autonomy. Distractor2 misses depression screening opportunity. Distractor3 focuses on less immediate concern. Distractor4 is premature without comprehensive screening and counseling first.
Q6A 20-month-old girl is brought to the office because her parents are concerned about her development. She speaks only 5 single words and does not combine words. She can walk well and run, but she does not yet walk up stairs. She feeds herself with a spoon and drinks from a cup. She points to objects she wants and waves bye-bye. Physical examination shows normal growth parameters and no dysmorphic features. Which of the following is the most appropriate management at this time?
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✓ Correct answer: Refer to early intervention and audiology for language delay evaluation
A 20-month-old should have 10-25 words and be starting to combine two words (expected by 24 months). Isolated language delay with normal social and motor skills still requires early intervention referral (IDEA Part C) and audiology evaluation to rule out hearing loss. Early intervention maximizes outcomes. Distractor1 inappropriately delays intervention beyond critical window. Distractor2 misses the early intervention opportunity. Distractor3 is premature without hearing evaluation. Distractor4 represents watchful waiting when action is indicated.
Q7A 30-month-old boy is brought to the office for a well-child visit. His father is concerned because the child does not yet speak in sentences. Review of developmental milestones shows the following findings: Domain Current Abilities Expected by 24 Months Expected by 36 Months Language 15 single words, no phrases Two-word phrases, 50+ words Three-word sentences, 200+ words Social Points, shares toys, parallel play Parallel play, imitates adults Cooperative play, takes turns Motor Runs well, kicks ball, walks stairs Runs, kicks ball, walks stairs Rides tricycle, alternates feet on stairs Cognitive Names pictures, sorts shapes Follows two-step commands Knows colors, understands concepts
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✓ Correct answer: Significant language delay with normal social and motor development
This child has isolated expressive language delay (no two-word phrases by 30 months, expected by 24 months) but normal social (parallel play, sharing) and motor milestones (runs, kicks ball, stairs). This pattern suggests specific language impairment rather than global developmental delay or autism. Requires early intervention and audiology referral. Distractor1 mischaracterizes as global delay when other domains are appropriate. Distractor2 describes normal development. Distractor3 incorrectly identifies autism when social skills are intact. Distractor4 reverses the delay pattern.
Q8A 30-year-old woman, gravida 2, para 1, at 28 weeks' gestation comes to the office for a routine prenatal visit. She received Tdap vaccine during her first pregnancy 3 years ago. She received her annual influenza vaccine 2 weeks ago. She asks about vaccinations needed during this pregnancy to protect her newborn. Her immunization record shows she is up to date on all routine adult vaccines. Which of the following is the most appropriate recommendation regarding pertussis vaccination?
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✓ Correct answer: Administer Tdap vaccine during this pregnancy, preferably at 27-36 weeks' gestation
Tdap is recommended during each pregnancy (preferably 27-36 weeks) to maximize transplacental antibody transfer and provide neonatal pertussis protection, regardless of previous vaccination history. Maternal antibodies wane, so repeat vaccination optimizes infant protection during vulnerable early months before infant series completion. Distractor1 is outdated guidance (one-time adult Tdap no longer sufficient for pregnancy). Distractor2 misses optimal timing for antibody transfer. Distractor3 represents inappropriate delay. Distractor4 confuses postpartum timing with prenatal recommendation.
Q9An 8-month-old girl is brought to the office for evaluation of inadequate weight gain. Her mother reports the infant is breastfed on demand but seems uninterested in feeding and often falls asleep after a few minutes. The family recently moved and the mother admits to feeling overwhelmed and isolated. Birth weight was 3.2 kg (50th percentile). Current weight is 6.0 kg (below 5th percentile for age). Physical examination shows a thin infant with decreased subcutaneous fat but no edema, organomegaly, or dysmorphic features. She is alert but does not smile readily. Which of the following is the most appropriate initial evaluation approach? Evaluation Component Specific Elements Priority History Feeding schedule, intake volume, formula preparation, caregiver stress, food insecurity High Physical Exam Signs of chronic disease (cardiac murmur, hepatomegaly), skin changes, developmental assessment High Initial Labs CBC, comprehensive metabolic panel, urinalysis, thyroid function Medium Specialized Testing Sweat chloride, celiac panel, imaging studies Low (if above unrevealing)
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✓ Correct answer: Comprehensive feeding history and psychosocial assessment before laboratory testing
Most failure to thrive cases result from inadequate caloric intake due to psychosocial factors (food insecurity, caregiver depression, feeding problems) rather than organic disease. Initial evaluation should focus on detailed feeding history, observation of feeding, and assessment of psychosocial stressors before extensive laboratory workup. The mother's report of feeling overwhelmed and the infant's disinterest in feeding suggest psychosocial contributors. Distractor1 is premature without history. Distractor2 represents overly aggressive testing. Distractor3 misses psychosocial factors. Distractor4 delays necessary nutritional intervention.
Q10A 2-week-old infant is brought to the office for a routine health supervision visit. The parents are first-time parents and ask for guidance on keeping their baby safe. The infant was born at term with no complications and is exclusively breastfed. Physical examination shows a healthy-appearing newborn with normal growth parameters. Which of the following safety counseling topics is most appropriate to emphasize at this visit?
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✓ Correct answer: Supine sleep position in smoke-free environment with firm sleep surface
For newborns and young infants, safe sleep counseling (supine position, firm surface, no soft bedding, smoke-free environment) is the highest priority to reduce SIDS risk. This is evidence-based injury prevention for this age group. Distractor1 addresses older infant safety (6+ months for solid foods). Distractor2 is important but less immediately relevant than safe sleep. Distractor3 is appropriate for toddlers. Distractor4 applies to older infants who are mobile.
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