Free USMLE Step 3 Exam Flashcards

Sensitivity = true positives / (true positives + false negatives). A highly sensitive test, when negative, effectively rules OUT disease (mnemonic: SnNout) because it misses very few true cases.

PPV = TP / (TP + FP) depends on disease prevalence. In a low-prevalence population, false positives make up a larger share of all positive results, so PPV drops even though sensitivity and specificity — properties intrinsic to the test — stay the same.

NNT = 1 / absolute risk reduction (ARR). A lower NNT means fewer patients must be treated to prevent one additional adverse outcome, indicating a more effective (or more clinically impactful) intervention.

Odds ratios are used in case-control studies, where cases and controls are selected by the investigator so true incidence cannot be directly measured. Relative risk requires a cohort or randomized trial design where incidence is directly observed.

A confounder is associated with both exposure and outcome and distorts the crude association when not accounted for — adjusting or stratifying for it should make the spurious association weaken or disappear. An effect modifier produces genuinely different effect sizes across subgroups; you report it stratified rather than adjusting it away.

CYP3A4 inhibition slows simvastatin metabolism, raising serum drug concentration and increasing the risk of myopathy and rhabdomyolysis — a classic drug-interaction application of foundational pharmacokinetics.

The displaced drug's free (unbound, pharmacologically active) fraction rises acutely, transiently increasing its effect and toxicity risk even though total drug concentration is unchanged — a foundational pharmacokinetics concept tested through clinical drug-interaction vignettes.

Respect the informed refusal. A patient with decision-making capacity has the right to refuse any treatment, even life-saving ones, once they understand the risks, benefits, and alternatives — autonomy takes priority over beneficence here.

(1) Communicate a choice, (2) understand the relevant information, (3) appreciate the situation and its likely consequences, and (4) reason through the information to reach a decision. Capacity is decision-specific and can fluctuate over time.

Common exceptions include emergency care, emancipated-minor status, and specific sensitive services such as STI treatment, contraception, substance-use treatment, and (in most states) outpatient mental health care — the exact list is state-specific, so physicians must know local statutes.

A systems-based ('Swiss cheese model') view of error: the mistake resulted from a latent system defect (label design), not solely individual negligence. The correct fix is a system-level change (e.g., tall-man lettering, barcode verification), not blaming the individual clinician.

Warfarin depletes protein C (a natural anticoagulant with a short half-life) faster than the procoagulant factors II, IX, and X, creating a transient hypercoagulable state that causes microvascular thrombosis in fatty tissue — classically seen in protein C deficiency and prevented by heparin bridging.

Idarucizumab is a monoclonal antibody fragment that directly binds and neutralizes dabigatran. Andexanet alfa is used instead for factor Xa inhibitors such as apixaban and rivaroxaban.

ACE inhibitors block bradykinin degradation, and bradykinin accumulation in the airway triggers cough. Switch to an angiotensin receptor blocker (ARB), which lowers blood pressure without affecting bradykinin metabolism.

Use free-text order entry and select the matching item from the auto-complete drop-down list rather than navigating multi-level menus — this mirrors realistic order entry and saves simulated and real time during the case.

Advance to the next necessary decision point (e.g., 'next appropriate time' or a specific interval) once all current orders are entered and there is nothing further to do immediately — but never skip past a point where a scheduled result or reassessment is due.

Failing to schedule appropriate reassessment after starting treatment — repeat vital signs, follow-up labs, or a return visit. CCS scoring rewards ongoing monitoring and timely response to a changing patient status, not just correct initial orders.

Posterior wall MI. ST depression with tall R waves in V1-V3 are reciprocal (mirror-image) changes of posterior ST elevation; confirm with posterior leads V7-V9 showing true ST elevation.

Less than 130/80 mmHg for most adults, per the 2017 ACC/AHA guideline, which also redefined stage 2 hypertension as ≥140/90 mmHg.

Oral anticoagulation is recommended (threshold is ≥2 in men, ≥3 in women). Direct oral anticoagulants (e.g., apixaban) are preferred over warfarin for most patients with nonvalvular AF.

HCM murmur INTENSIFIES with Valsalva/standing (reduced preload worsens dynamic outflow obstruction) and softens with squatting. Aortic stenosis is the opposite — the murmur softens with Valsalva/standing and intensifies with squatting (increased preload/afterload).

A CURB-65 score of ≥2 (Confusion, blood Urea >19 mg/dL, Respiratory rate ≥30/min, Blood pressure <90/60 mmHg, Age ≥65) suggests admission; a score of ≥3 suggests consideration of ICU-level care.

Order a D-dimer; if negative, PE is effectively excluded without further imaging. For a moderate/high pretest probability by Wells score, proceed directly to CT pulmonary angiography instead of D-dimer.

Bilateral opacities on chest imaging not fully explained by cardiac failure/fluid overload, arising within 1 week of a known insult, with PaO2/FiO2 ≤300. Severity is graded mild (200-300), moderate (100-200), and severe (≤100).

Short-acting bronchodilators (albuterol/ipratropium), a short course of systemic corticosteroids, and antibiotics when there is increased sputum purulence or a need for ventilatory support — this combination lowers relapse and treatment-failure rates.

qSOFA ≥2 of: respiratory rate ≥22/min, altered mentation, and systolic BP ≤100 mmHg. Meeting 2 or more criteria should prompt further sepsis workup and escalation of care.

Iron deficiency typically shows an elevated RDW (variable cell size) with low ferritin. Thalassemia trait typically shows a normal RDW with an MCV disproportionately low for the degree of anemia (Mentzer index, MCV/RBC count, <13) and normal-to-high iron stores.

Immediate empiric broad-spectrum antipseudomonal antibiotics (e.g., cefepime or piperacillin-tazobactam) within 1 hour of presentation, without waiting for culture results — delayed antibiotics increase mortality in this population.

Lactulose, titrated to 2-3 soft bowel movements per day; it acidifies the colon and traps ammonia as ammonium for fecal excretion. Rifaximin is added for recurrent or refractory episodes.

Endoscopy within 24 hours of presentation after hemodynamic resuscitation, for both diagnosis and therapeutic intervention (e.g., variceal banding, ulcer clipping) — sooner for hemodynamically unstable patients.

2 of 3: characteristic epigastric pain, lipase or amylase greater than 3x the upper limit of normal, and characteristic findings on imaging. Imaging is not required if the first two criteria are already met.

Osmotic demyelination syndrome (central pontine myelinolysis). The generally recommended safe limit is no more than 8 mEq/L per 24 hours, with an even slower rate in high-risk patients (chronic alcoholism, malnutrition, advanced liver disease, severe baseline hyponatremia).

Anion gap = Na+ − (Cl− + HCO3−), normal roughly 8-12 mEq/L. An elevated gap suggests accumulation of unmeasured acids (e.g., lactic acidosis, ketoacidosis, uremia, or toxic alcohol ingestion — mnemonic MUDPILES).

Preeclampsia with severe features. Magnesium sulfate is the first-line agent for eclampsia (seizure) prophylaxis — not a standard antiepileptic drug.

Avoid fluoroquinolones (cartilage/tendon toxicity risk) and avoid sulfamethoxazole-trimethoprim or nitrofurantoin near term (risk of neonatal hyperbilirubinemia/hemolysis). Nitrofurantoin or cephalexin are generally preferred earlier in pregnancy.

Ectopic pregnancy. A suboptimally rising or plateauing beta-hCG is concerning for a nonviable intrauterine pregnancy or an ectopic pregnancy; transvaginal ultrasound is used once hCG reaches the discriminatory zone to help localize the pregnancy.

Metformin, given its efficacy, weight neutrality, low hypoglycemia risk, and favorable cardiovascular safety profile. Renal function should be checked before starting and monitored periodically.

Potassium must be repleted first. Insulin drives potassium intracellularly and can precipitate life-threatening hypokalemia and arrhythmia; insulin is generally held until potassium is above about 3.3 mEq/L.

Subclinical hypothyroidism shows an elevated TSH with a NORMAL free T4. Overt hypothyroidism requires both an elevated TSH and a low free T4.

Generally within 4.5 hours of last known well, after excluding hemorrhage on noncontrast head CT and screening for other contraindications (the window was extended from the original 3 hours based on later trial data).

Lumbar puncture to look for xanthochromia (or CT angiography) to rule out subarachnoid hemorrhage — CT sensitivity for SAH drops significantly beyond about 6-12 hours from symptom onset.

'Wet, wobbly, and wacky': urinary incontinence, gait disturbance, and cognitive decline, with ventriculomegaly disproportionate to cortical atrophy on imaging. Gait disturbance is typically the first and most shunt-responsive symptom.

Botulinum toxin (Clostridium botulinum), which blocks presynaptic acetylcholine release at the neuromuscular junction causing descending, symmetric flaccid paralysis. Treatment is botulinum antitoxin.

Unlike most withdrawal syndromes, benzodiazepine withdrawal can cause life-threatening seizures. Management is a slow taper, or substitution with a long-acting benzodiazepine followed by gradual taper — never abrupt discontinuation.

Serotonin syndrome features hyperreflexia, myoclonus, and clonus, with rapid onset (hours) after a serotonergic agent. NMS features 'lead-pipe' rigidity and hyporeflexia, with slower onset (days) after a dopamine-blocking antipsychotic.

Negatively birefringent needle-shaped crystals indicate gout (monosodium urate). Positively birefringent rhomboid crystals indicate pseudogout (calcium pyrophosphate deposition disease).

Arthrocentesis for synovial fluid cell count, Gram stain, and culture, ideally before starting antibiotics. A synovial WBC count above roughly 50,000/microL with PMN predominance strongly suggests septic arthritis, a surgical and medical emergency.

Stevens-Johnson syndrome (SJS) — mucocutaneous sloughing under 10% body surface area defines SJS (10-30% is SJS/TEN overlap, over 30% is toxic epidermal necrolysis). Immediately discontinue the suspected offending drug.

Asymmetry, Border irregularity, Color variation, Diameter greater than 6mm, and Evolution over time. Any one of these features in a pigmented lesion raises suspicion for melanoma and warrants biopsy consideration.

The first dose is given at 12-15 months of age, with the second dose at 4-6 years. MMR is a live attenuated vaccine, so it is deferred in pregnancy and in significant immunosuppression.