USMLE Step 3 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Sensitivity

Proportion of patients with disease who test positive (TP/[TP+FN]). A highly sensitive test is used to rule out disease because false negatives are few.

Specificity

Proportion of patients without disease who test negative (TN/[TN+FP]). A highly specific test is used to rule in disease because false positives are few.

Positive predictive value

Probability that a positive test is correct (TP/[TP+FP]). It rises with disease prevalence, so the same test performs differently in high- versus low-prevalence populations.

Positive likelihood ratio

LR+ = sensitivity/(1 − specificity). Values above 10 markedly raise post-test probability; post-test odds equals pretest odds multiplied by the likelihood ratio.

Number needed to treat

Reciprocal of the absolute risk reduction (1/ARR). It estimates how many patients must be treated for one additional favorable outcome to occur.

Odds ratio

Ratio of exposure odds among cases to exposure odds among controls. Used in case-control studies and approximates relative risk when the outcome is rare.

Type I error

Probability of rejecting a true null hypothesis (alpha, usually 0.05). It is equivalent to a false-positive conclusion that a difference exists when none does.

Statistical power

Probability of detecting a true difference (1 − beta), conventionally 80%. Power increases with larger sample size, larger effect size, and lower outcome variability.

Lead-time bias

Apparent survival gain from screening because diagnosis occurs earlier without postponing death. Survival measured from diagnosis looks longer despite unchanged natural history.

Length-time bias

Screening preferentially detects slowly progressive disease with a long preclinical phase, inflating apparent survival independent of any true screening benefit.

Phase III trial

Large randomized trial comparing a new intervention with the current standard in patients who have the target condition; it is the usual basis for drug approval.

Medicare eligibility

Federal insurance for people aged 65 or older and for those with end-stage renal disease or amyotrophic lateral sclerosis, regardless of income.

Informed consent elements

Requires patient capacity, disclosure of risks, benefits and alternatives, comprehension, and voluntariness; a signature documents but does not replace the discussion.

Tarasoff duty

Duty to warn and protect an identifiable third party when a patient makes a credible serious threat of violence; confidentiality yields to this duty.

Intention-to-treat analysis

Analysis that assigns participants to the group they were randomized to regardless of adherence. It preserves randomization and avoids bias from noncompliance or dropout.

Incidence

Number of new cases arising in a population at risk over a specified period. It measures risk and is preferred for causal inference, unlike prevalence.

Door-to-balloon time

For STEMI treated with primary PCI, the goal is 90 minutes or less from hospital arrival to device activation; fibrinolysis within 30 minutes if PCI is unavailable.

Stroke thrombolysis window

IV alteplase or tenecteplase may be given up to 4.5 hours from last known well, with a door-to-needle target of 60 minutes or less, if blood pressure is below 185/110.

Sepsis fluid resuscitation

Give 30 mL/kg of balanced crystalloid for sepsis-induced hypotension or lactate of 4 mmol/L or higher, then reassess; start broad-spectrum antibiotics within one hour.

DKA insulin protocol

Start IV regular insulin at 0.1 units/kg/h after confirming potassium is at least 3.3 mEq/L; add dextrose when glucose falls below 200-250 mg/dL.

Hyperkalemia with ECG changes

Give IV calcium gluconate first to stabilize the myocardium, then shift potassium intracellularly with insulin/glucose and albuterol; remove potassium with diuretics or dialysis.

Hyponatremia correction limit

For chronic hyponatremia, raise sodium by no more than 8-10 mEq/L in 24 hours to avoid osmotic demyelination; symptomatic patients receive hypertonic 3% saline boluses.

COPD oxygen target

Titrate oxygen to an SpO2 of 88-92% in patients at risk of hypercapnic respiratory failure; give bronchodilators, systemic steroids, antibiotics, and noninvasive ventilation.

CHA2DS2-VASc threshold

Anticoagulate atrial fibrillation when the score is 2 or more in men or 3 or more in women; consider anticoagulation at 1 in men or 2 in women.

Acute pancreatitis management

Aggressive lactated Ringer solution, early enteral feeding, and analgesia. Prophylactic antibiotics are not indicated in the absence of infection or cholangitis.

Upper GI bleed

Resuscitate, give an IV proton pump inhibitor, and perform endoscopy within 24 hours; transfuse to a hemoglobin around 7-8 g/dL unless there is cardiovascular disease.

Thyroid storm treatment

Give propylthiouracil first, iodine at least one hour later, plus a beta-blocker and hydrocortisone; treat fever and volume depletion with supportive care.

Adrenal crisis treatment

Give hydrocortisone 100 mg IV immediately, with isotonic saline and dextrose. Do not delay steroids to obtain confirmatory cortisol and ACTH testing.

Meningitis empiric therapy

Vancomycin plus ceftriaxone, adding ampicillin for adults over 50 or immunocompromised patients; give dexamethasone with or before the first antibiotic dose.

Status epilepticus first line

IV lorazepam 0.1 mg/kg (maximum 4 mg) is first line; if seizures persist, give a second benzodiazepine then fosphenytoin, levetiracetam, or valproate.

Unstable pulmonary embolism

Treat with thrombolysis, catheter-directed therapy, or surgical embolectomy plus anticoagulation; hemodynamically stable PE is treated with anticoagulation alone.

Alcohol withdrawal treatment

Benzodiazepines are first line, dosed by symptom-triggered scores; give thiamine before glucose to prevent Wernicke encephalopathy in at-risk patients.