In series testing, which statement is true?

• A. The test is positive if either test is positive.
• B. The test is declared negative only if both tests are negative.
• C. The approach increases false negatives.
• D. The approach requires both tests to be positive to declare disease.

Answer: (D)

In serial (or series) testing, the essential rule is that disease is declared only if both tests are positive. This means you require confirmation from two independent tests before labeling someone as diseased, which lowers the chance of a false positive and increases specificity compared with using a single test or a parallel approach. However, this comes at the cost of potentially missing true cases if one test misses the disease, leading to more false negatives. The other statements describe scenarios that don’t match the serial-testing rule: one applies to parallel testing (positive if either test is positive), another describes declaring negative only if both are negative (not how serial testing is interpreted), and the remaining point is a consequence of serial testing rather than its defining rule.