Westgard Rules measurements per run are generally used with how many control measurements per run?

• A. Two
• B. One
• C. Five or Six
• D. Ten

Answer: (A)

Westgard multirule QC relies on looking at a sequence of control measurements to decide if a run is in control. Two control measurements per run provide the minimum data points needed to apply the common rules that detect both random and systematic errors. With only one control result, you can’t assess patterns across the run (such as consecutive results drifting or crossing decision limits). Having two controls—often a normal and a different-control level—lets you evaluate patterns like two consecutive results beyond a threshold or the difference between controls, which are central to these rules. In practice, this is why labs typically run two control measurements per run. Larger numbers of controls per run aren’t usually required for the standard Westgard rules, though more data can enhance detection.