What are Westgard rules and how do they help monitor assay performance?

• A. Statistical QC criteria to detect systematic or random error; examples include 1-2s, 2-2s, 4-1s, and 12s patterns used to decide when to reject a run
• B. Guidelines for sample collection
• C. Steps of Gram stain
• D. Serial dilution calculations

Answer: (A)

Westgard rules are a set of statistical quality control criteria used in clinical labs to judge whether an assay is performing acceptably based on control measurements. They help detect both random errors, which cause scatter around the target, and systematic errors, such as drift or a consistent bias over time. By evaluating control results against predefined limits and looking for patterns across recent measurements, these rules provide a structured way to decide when a run should be rejected and investigated.

In practice, control measurements are run with patient testing to establish that the assay system is behaving as expected. If a control result falls outside the acceptable range, that flags a potential problem with the method, instrument, or reagents. If there’s a pattern in the control data—such as a drift, a shift, or a nonrandom sequence—the rules signal that reliability may be compromised, prompting action before patient results are reported.

This approach balances sensitivity to real errors with the need to avoid unnecessary rechecks, helping maintain accurate and reliable test results over time.

Other options describe topics unrelated to assay performance monitoring, such as how samples are collected, steps in Gram staining, or calculations for serial dilutions.