A mass screening programme for hypertension in a district uses a cut-off of SBP ≥ 140 mmHg. If the programme committee decides to lower the cut-off to SBP ≥ 130 mmHg, the net effect on the screening test performance would be:
- A Sensitivity decreases; specificity increases; more false negatives
- B Sensitivity increases; specificity decreases; more false positives ✓
- C Both sensitivity and specificity increase simultaneously
- D Sensitivity decreases; specificity decreases; more true negatives
Correct answer: B. Sensitivity increases; specificity decreases; more false positives
Explanation
Lowering a cut-off value for a test designed to screen for a high-value condition (where positive = high SBP) means more individuals are classified as test-positive. This increases sensitivity (fewer missed cases, fewer false negatives) but decreases specificity (more non-hypertensive individuals are falsely labeled as hypertensive, increasing false positives). Sensitivity and specificity are inversely related along the ROC curve as the cut-off is moved.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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