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Screening test threshold — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsScreening test thresholdUSMLE Step 3

A hospital lowers the D-dimer threshold that triggers CT pulmonary angiography. More pulmonary emboli are detected, but more patients without embolism also have a positive test. Which test-performance change best explains this?

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Correct answer: E — Sensitivity increases and specificity decreases

Lowering a positive threshold captures more true positives and more false positives, increasing sensitivity while lowering specificity. Predictive value still depends on the prevalence in the tested population.

Reference: CDC, Principles of Epidemiology in Public Health Practice: https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section6.html