Two screening tests are applied sequentially for the same disease, and a subject is considered positive only if both tests are positive. Test A has sensitivity 90% and specificity 80%. Test B has sensitivity 80% and specificity 90%. What is the combined (net) sensitivity of this sequential strategy?
- A 98%
- B 72% ✓
- C 85%
- D 94%
Correct answer: B. 72%
Explanation
In series (sequential) testing, net sensitivity equals the product of individual sensitivities: 0.90 multiplied by 0.80 gives 0.72, that is 72%. The tempting option 98% is actually the net specificity of this sequence (calculated as SpA plus SpB minus their product). Sequential testing therefore raises specificity at the cost of sensitivity, the opposite of parallel testing.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.