A COVID test is performed on 3,000 patients. Results: Sick patients: 850 positive, 10 negative. Healthy patients: 40 positive, 2,100 negative. What is the SENSITIVITY of the test?

Correct answer: A. ~99% (850 true positives / (850+10) total sick = 850/860 = 98.8%)

• A. Correct. SENSITIVITY = TP/(TP+FN) = True positives/(True positives + False negatives). TP = 850 (sick and test positive), FN = 10 (sick but test negative). Sensitivity = 850/(850+10) = 850/860 = 0.988 = ~99%. This means the test correctly identifies 99% of truly sick patients.
• B. 95% would imply 43 false negatives — actual FN is 10, giving higher sensitivity.
• C. 90% would imply 86 false negatives out of 860 sick — the actual FN is only 10.
• D. 80% would require many more false negatives — not consistent with these numbers.