The Waning rule to trigger careful inspection of the following control results corresponds to which Westgard rule?

• A. 1(2s) Westgard Rules
• B. 1(3s) Westgard Rules
• C. 2(2s) Westgard Rules
• D. R(4s) Westgard Rules

Answer: (A)

A warning rule is being tested here. It triggers when a single control result falls outside ±2 standard deviations from the target. This serves as an early signal to inspect the assay performance, calibration, reagents, or instrument conditions before proceeding, but it doesn’t by itself reject the run.

That’s why the rule described by a single point beyond 2 SD is the appropriate match. Other options describe different criteria: a single point beyond 3 SD is a stricter action level, two consecutive points beyond 2 SD on the same side indicate a more definite issue, and a range exceeding 4 SD uses the difference between adjacent results to flag problems.