Sensitivity rules OUT means what?

• A. A negative result helps rule out disease
• B. A positive result rules out disease
• C. Neither affects probability
• D. It only applies to high prevalence

Answer: (A)

When a test is highly sensitive, a negative result is used to rule out disease. Sensitivity refers to how good the test is at identifying people who have the disease—high sensitivity means few false negatives. So if the test comes back negative, it’s unlikely the person actually has the disease, and you can confidently rule it out. This is why the correct interpretation is that a negative result helps rule out disease. The other ideas aren’t correct because a positive result doesn’t rule out disease, prevalence doesn’t determine this rule-out property, and a negative result does change the probability of disease (it lowers it), not leaves it the same.