Screening test principles in children — branching viva

Opening

Examiner prompt and strong answer — definition: Screening offers tests to apparently well children to find unrecognised disease or risk early enough that planned action improves outcomes. Diagnostic testing answers what is wrong in a symptomatic child. A screen is a programme step, not a diagnosis. [4]

Branch A — Criteria

Examiner prompt and strong answer — is high sensitivity enough? No. Apply programme criteria: important conditions, acceptable tests, effective early treatment, pathway capacity, quality assurance, informed choice, equity, and net benefit after harms. Detection alone is not benefit. [1] [2] [3]

Examiner prompt and strong answer — harms to count: False-positive cascades with anxiety and procedures; overdiagnosis of mild non-harmful variants; opportunity cost; inequitable incomplete follow-up. [7] [8] [6]

Branch B — Numbers

Examiner prompt and strong answer — low PPV despite high specificity: In low prevalence, the well population is huge. Absolute false positives can outnumber true positives among those who flag positive, so most positives may not be disease. [5]

Branch C — Communication

Examiner prompt and strong answer — parents want the free panel: Acknowledge the wish for reassurance. Explain that unselected multi-disease panels can create more noise than help without pathways. Offer established high-value programme screens that your service can complete properly. Document decline of low-value testing without coercion. [2] [6]

Close

Examiner prompt and strong answer — policy line: Do not implement population screening unless criteria, pathway capacity and net benefit are demonstrated and auditable. [2] [3]