A screening test for diabetes has a sensitivity of 85% and specificity of 70%. In a community where the prevalence of diabetes is 5%, the Positive Predictive Value (PPV) of this test is closest to:
- A 85%
- B 13% ✓
- C 23%
- D 5%
Correct answer: B. 13%
Explanation
Using a hypothetical cohort of 10,000: True positives = 5% × 10,000 × 0.85 = 425; False positives = 95% × 10,000 × 0.30 = 2850; PPV = 425/(425+2850) = 425/3275 ≈ 13%. This illustrates Bayes' theorem: even a moderately sensitive and specific test yields low PPV when disease prevalence is low (5%). This is the fundamental principle behind why population-level screening of low-prevalence diseases generates many false positives and requires confirmation testing.
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.