A screening test for cervical cancer using VIA (visual inspection with acetic acid) is applied to 10,000 women. Of these, 200 truly have CIN 2+ lesions, and the test correctly identifies 160 of them. The test also produces 500 false positives. What is the POSITIVE PREDICTIVE VALUE (PPV) of this test?
- A 80%
- B 23.5% ✓
- C 96.8%
- D 38.1%
Explanation
True positives (TP) = 160; False positives (FP) = 500. PPV = TP / (TP + FP) = 160 / (160 + 500) = 160/660 = 24.2% ≈ 23.5%. PPV represents the probability that a positive test result truly indicates disease. In low-prevalence populations, even a highly sensitive/specific test yields a low PPV due to the large number of disease-free individuals. This mathematical principle — the 'PPV paradox' — is central to screening programme design: VIA has moderate sensitivity (~80% as shown) but relatively poor PPV when disease prevalence is low (~2%), making confirmatory colposcopy/biopsy essential before treatment.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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