USMLE Step 3 key terms

The proportion of people who truly have a condition and are correctly identified by a test as positive. High sensitivity means few false negatives, so a negative result helps rule out disease.

The proportion of people without the condition who are correctly identified by a test as negative. High specificity means few false positives, so a positive result helps rule in disease.

The probability that a person with a positive test result actually has the condition. It depends on disease prevalence, so the same test can give different values in different populations.

A number showing how much a test result changes the odds of disease. A positive likelihood ratio above 1 raises the odds, while a negative ratio below 1 lowers them.

The number of patients who must receive a treatment for one additional patient to benefit. It is the inverse of the absolute risk reduction, and smaller values mean a larger treatment effect.

The ratio of the risk of an outcome in an exposed group to the risk in an unexposed group. A value above 1 suggests increased risk, while a value below 1 suggests protection.

The ratio of the odds of an exposure in people with a disease to the odds of exposure in people without it. It is common in case-control studies and approximates relative risk for rare diseases.

A range of values likely to contain the true population estimate, calculated from sample data. A 95% interval means that 95% of similarly built intervals would include the true value.

Rejecting a true null hypothesis, often called a false-positive finding. Its probability is alpha, commonly set at 0.05, meaning a 5% chance of making this error.

Failing to reject a false null hypothesis, often called a false-negative finding. Its probability is beta; study power equals 1 minus beta, the chance of detecting a true effect.

An analysis that includes all participants in the groups to which they were originally assigned, even if they did not follow the protocol. It preserves randomization and estimates real-world effectiveness.

The apparent survival gain caused by detecting disease earlier, even when treatment does not change the time of death. It makes screening programs look more effective than they truly are.

The tendency of screening to find slower-growing, less aggressive disease more often than fast-growing disease. This makes screened patients seem to live longer even when screening has no real benefit.

A third variable linked to both the exposure and the outcome that distorts the observed relationship between them. Randomization, restriction, stratification, or statistical adjustment can reduce its effects.

The number of new cases of a disease that develop in a population during a specified period. It measures how quickly new disease occurs and is useful for studying causes.

The proportion of a population that has a disease at a given time or during a period. It reflects both new and existing cases and is influenced by incidence and disease duration.

A study in which participants are randomly assigned to receive one of two or more interventions. Randomization balances known and unknown confounders, making causal conclusions stronger than in observational studies.

The process of explaining a proposed medical intervention to a patient, including risks, benefits, alternatives, and consequences of refusal, and obtaining voluntary agreement. It requires decision-making capacity and should be documented.

A patient's ability to understand relevant information, appreciate the consequences of choices, reason about options, and communicate a consistent decision. It is decision-specific and assessed by clinicians, unlike legal competence.

A legal document in which a person records preferences for future medical care or names someone to decide if they lose capacity. Living wills and health care powers of attorney are common forms.

A structured team method for investigating a serious adverse event to find underlying system failures rather than blaming individuals. Its goal is to redesign processes and prevent recurrence.

Testing apparently healthy people to find disease before symptoms appear, aiming for earlier treatment and better outcomes. Effective screening requires a common condition, an acceptable test, and proven benefit.

A life-threatening organ dysfunction caused by a dysregulated host response to infection. It is recognized by infection plus organ dysfunction and requires prompt antibiotics, fluids, and source control.

Sepsis with persistent hypotension that requires vasopressors to maintain adequate blood pressure and a high lactate level despite fluid resuscitation. It carries high mortality and needs intensive care.

A spectrum of conditions caused by a sudden reduction in coronary blood flow, including unstable angina and myocardial infarction. Patients often present with chest pain, diaphoresis, and shortness of breath.

A heart attack caused by complete coronary artery occlusion and diagnosed by ST-segment elevation on electrocardiography. Emergency reperfusion with percutaneous coronary intervention or fibrinolysis is needed to limit heart damage.

A clinical syndrome of congestion or low perfusion caused by impaired ventricular pumping, with left ventricular ejection fraction of 40% or less. Guideline-directed medical therapy improves survival.

An irregularly irregular supraventricular rhythm caused by chaotic atrial electrical activity. It raises stroke risk and is managed with rate or rhythm control plus anticoagulation when indicated.

A condition encompassing deep vein thrombosis and pulmonary embolism, caused by blood clot formation in veins. Risk factors include immobility, surgery, cancer, and hypercoagulable states.

An infection of the lung tissue acquired outside a hospital, causing fever, cough, sputum, and dyspnea. Severity scores help decide outpatient versus inpatient care and guide antibiotic selection.

A metabolic emergency marked by high blood glucose, ketosis, and a high-anion-gap metabolic acidosis, usually from insulin deficiency. Treatment involves intravenous fluids, insulin, and potassium replacement.

A severe hyperglycemic emergency with very high serum osmolality, profound dehydration, and little or no ketosis. It occurs mainly in older adults with type 2 diabetes and needs careful fluid and insulin therapy.

A sudden decline in kidney function shown by rising creatinine or falling urine output. Causes are prerenal, intrinsic renal, or postrenal; management focuses on the cause and preventing complications.

An acute, fluctuating disturbance of attention and awareness often caused by illness, medications, or withdrawal. It is common in hospitalized older adults and requires treating the cause and reducing risk factors.

Advanced liver scarring that distorts architecture and impairs function, causing portal hypertension and synthetic failure. Complications include ascites, varices, encephalopathy, and spontaneous bacterial peritonitis.

Severe blood pressure elevation with acute target-organ damage such as encephalopathy, aortic dissection, pulmonary edema, or renal injury. It requires controlled reduction of blood pressure, often with intravenous medication.

A rapid, severe systemic allergic reaction that can cause airway swelling, bronchospasm, hypotension, and rash. Intramuscular epinephrine is the first-line treatment.

A syndrome after stopping or reducing heavy alcohol use, ranging from tremor and anxiety to seizures and delirium tremens. Benzodiazepines are first-line treatment for significant symptoms.