A new screening test for colorectal cancer is introduced in a community. It has high sensitivity but modest specificity. The MOST important consequence of low specificity in a mass screening programme is:

• A Missing of true cases leads to delayed treatment and worse outcomes
• B High false-positive rate leads to unnecessary invasive diagnostic procedures, anxiety, and costs ✓
• C Reduced sensitivity of subsequent confirmatory tests
• D Overestimation of disease prevalence in the population

Explanation

Low specificity means a high false-positive rate (many disease-free individuals test positive). In mass screening, this leads to large numbers of healthy people being referred for invasive confirmatory procedures (e.g., colonoscopy for false-positive FOBt), causing procedural complications, anxiety, psychological harm, and significant healthcare costs. Missing true cases (option A) results from low sensitivity, not low specificity. Reduced sensitivity of confirmatory tests (option C) is not a direct consequence. Prevalence estimation error (option D) occurs with both false positives and false negatives but the primary operational harm of low specificity is unnecessary downstream investigation.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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