Laboratory and imaging
Westgard rules
Westgard rules are a set of statistical control rules, applied to quality control results plotted on a Levey Jennings chart, that tell a laboratory whether an analytical run is in control and whether its patient results can be released.
Why it matters
Every analytical method drifts over time. Quality control detects that drift before it reaches patient results, and Westgard rules give staff an objective basis for accepting or rejecting a run. Used together as a multirule procedure, the rules detect both random and systematic error while keeping false rejections low [1].
Key points
- 1:3s: one control result exceeds 3 SD from the mean, indicating random error [1].
- 2:2s: two consecutive control results exceed 2 SD on the same side of the mean, indicating systematic error [1].
- R:4s: the difference between two controls in the same run exceeds 4 SD, indicating random error [1].
- 4:1s and 10:x: four consecutive results beyond 1 SD, or ten on the same side of the mean, indicating systematic error [2].
- In the classic procedure 1:2s is a warning rule, and current guidance favours choosing rules for each test by its Sigma performance [3].
In Moana
MOANA LIS applies Westgard rules to control results captured with each run, plots them on Levey Jennings charts and records the outcome against the run.
Sources
- Basic QC practices: lesson on Levey Jennings charts and control rules, Westgard QC, accessed 2026
- Fifty ways to apply Westgard rules, Westgard QC, accessed 2026
- When is it time to wean yourself off warning rules?, Westgard QC, 2025
Read the guide: Laboratory Quality Control: Westgard Rules and Levey Jennings Charts
In the platform: MOANA LIS
Related terms: Levey Jennings chart, Laboratory information system, Critical value
Updated 2026-11-03. Written under Moana’s editorial standards.