Two screening tests are applied sequentially for breast cancer. Test A has sensitivity 80% and specificity 90%. Test B has sensitivity 70% and specificity 95%. A woman must be positive on both tests to be called screen-positive. The combined specificity of this sequential strategy is approximately:
- A 85.5%
- B 56%
- C 99.5% ✓
- D 94.5%
Correct answer: C. 99.5%
Explanation
In serial testing a person is positive only if positive on both tests, so she must be negative on neither. Combined specificity equals 0.90 multiplied by 0.95, that is 99.5%. Combined sensitivity falls to 0.80 multiplied by 0.70, only 56%. This trade-off, higher specificity at the cost of sensitivity, is exactly why serial strategies suit confirmatory pathways where false positives carry heavy costs such as invasive follow-up.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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