Specificity and false positives — MRCPCH TAS MCQ

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ModerateStatistics and evidence-based medicineSpecificity and false positivesMRCPCH TAS

A screening blood test for a rare metabolic disease causes considerable parental anxiety after false positive results. The laboratory wants fewer unaffected babies to test positive. Which test characteristic should improve?

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Correct answer: D — Specificity

Specificity is the proportion of unaffected individuals who test negative, so higher specificity reduces false positives. Sensitivity addresses false negatives rather than false positives. The pearl is that in rare diseases, even a specific test may have a lower positive predictive value than expected.

Reference: The Science of Paediatrics MRCPCH Mastercourse; CEBM diagnostic test principles; RCPCH Theory examination syllabi