Westgard rules for clinical QC, explained
Westgard rules are the statistical patterns a clinical laboratory uses to decide whether a quality-control (QC) run is in-control or out-of-control. First published by James Westgard in Clinical Chemistry in 1981, the six base rules — 1-2s, 1-3s, 2-2s, R-4s, 4-1s, 10-x — combine into multi-rule sets that catch both random and systematic analytical errors with a low false-rejection rate. This post is a working reference: the precise trigger condition for each rule, the clinical interpretation, why 1-2s is a warning rather than a rejection, the canonical multi-rule set, and how to read a Levey-Jennings chart that visualises everything together. This post is a standalone primer for anyone who needs the rules, independent of any product.
:::note LabFlow does not implement quality control today Quality control is planned and unbuilt — see the roadmap. Nothing below describes a LabFlow feature. :::