Sensitivity/Specificity — MCQs

A pharmaceutical company develops a sequential testing protocol for a rare genetic disorder (prevalence 0.01%). Initial screening test has sensitivity 95% and specificity 90%. Positive results undergo confirmatory testing with sensitivity 99% and specificity 99.5%. The company claims this approach achieves PPV >80% for the final positive result. Evaluate this claim and the rationale for sequential testing in this context.

A hospital system is implementing a sepsis screening algorithm using clinical criteria with sensitivity of 92% and specificity of 75%. False positives result in unnecessary antibiotics, cultures, and ICU evaluations costing $3,000 per case. Missing true sepsis cases (false negatives) results in average increased mortality and morbidity costs of $50,000 per case. Hospital sepsis prevalence is 8%. Evaluate the optimal threshold adjustment strategy.

A 58-year-old man with chronic cough undergoes evaluation for tuberculosis. A tuberculin skin test (TST) is positive (15mm induration). TST has sensitivity of 80% and specificity of 95% in immunocompetent adults. However, he received BCG vaccination as a child in Asia. Local TB prevalence is 0.5%, but his occupational exposure increases his pre-test probability to 10%. Evaluate the most appropriate interpretation and management approach.

A research team develops a novel biomarker for early Alzheimer's disease. In their validation study of 500 patients with confirmed Alzheimer's and 500 age-matched controls, the biomarker is positive in 450 Alzheimer's patients and 50 controls. They plan to use this test in a memory clinic where 30% of patients have Alzheimer's. Analyze how the test performance will differ in the clinical setting compared to the validation study.

A 35-year-old woman presents with fatigue and is found to have a positive antinuclear antibody (ANA) test. The test has sensitivity of 95% and specificity of 85% for systemic lupus erythematosus (SLE). She has no other symptoms or physical findings suggestive of SLE. The prevalence of SLE in asymptomatic women her age is 0.1%. Analyze the significance of her positive test result.