When the cut-off value for a screening test is shifted to lower levels (e.g., lowering blood glucose threshold for diabetes screening), which paired change occurs?

• A Sensitivity decreases and specificity increases
• B Both sensitivity and specificity increase
• C Sensitivity increases and specificity decreases ✓
• D PPV increases while NPV decreases

Explanation

When the threshold is lowered (more liberal cut-off), more individuals test positive, including true cases that would have been missed (increased sensitivity) but also more false positives from healthy individuals (decreased specificity). This is the fundamental trade-off in screening test thresholds visualised by the ROC curve. For mass screening of severe diseases (e.g., cancer, HIV), higher sensitivity is preferred even at the cost of specificity; for confirmatory testing, higher specificity is preferred.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.