What term describes the combination of decision criteria used to decide whether an analytical run is in-control or out-of-control?

• A. Cusum, in control
• B. Westgard Rules
• C. R(4s) Westgard Rules
• D. 10x Westgard Rules

Answer: (B)

Westgard Rules are the set of decision criteria used to decide whether a laboratory QC run is in control or out of control. They combine multiple rule checks across successive control measurements to detect random errors, shifts, and trends, providing a structured way to interpret when a run should be accepted or rejected. By applying these rules together, the lab can balance sensitivity to real problems with avoiding false alarms. Examples of these rules include general checks against single results outside a threshold, patterns of consecutive results on one side of the mean, and combinations that flag when multiple criteria are violated within a run. Cusum, by contrast, is a different monitoring approach that tracks cumulative deviations over time rather than a predefined set of QC decision criteria, so it’s not the same framework. Specific rules like R(4s) or 10x are components within the Westgard system, but the overall term that describes the entire combination of decision criteria is Westgard Rules.