Overview
Westgard rules are practical decision flags used on QC control charts. Each rule describes a visual pattern relative to the mean and s-lines. Local SOP determines which rules are active and what actions follow.
Classification
| Rule | What you see | Typical action |
|---|---|---|
| 1-2s | One point beyond 2s | Warning, follow SOP (watch/check) |
| 1-3s | One point beyond 3s | Reject / hold; troubleshoot |
| 2-2s | Two consecutive beyond 2s, same side | Reject / hold; investigate shift |
| R-4s | Two points in run differ by ~4s | Reject / hold; imprecision concern |
| 4-1s | Four consecutive beyond 1s, same side | Reject / hold; shift/trend |
| 10x | Ten consecutive on same side of mean | Reject / hold; persistent shift |
Morphologic Features
Not applicable, this entry covers QC decision rules, not morphology.
Laboratory Characteristics
- Often implemented in instrument/middleware software
- Warning vs reject depends on SOP configuration
- Document which rule fired and the action taken
Reference Intervals
Not a patient reference interval. Chart lines (1s/2s/3s) are QC performance guides for control materials, defined for the method and laboratory practice.
Clinical and Laboratory Significance
Ignoring reject-rule flags can release unreliable results. Treating Westgard as optional math trivia undermines daily patient protection.
Differential Considerations
Not a disease differential. Separate warning flags (often 1-2s) from reject patterns, and confirm the active rule set in the local SOP before acting.
Comparison Tables
Westgard practical checkpoints
| Habit | Safe practice | Unsafe shortcut |
|---|---|---|
| Rule fires | See → SOP meaning → act/document | Release because patients 'look fine' |
| Unsure which rules apply | Check assay SOP / ask supervisor | Assume every published rule is active |
| 1-2s vs 1-3s | Treat per SOP (often warn vs reject) | Ignore both as 'statistics' |
Classification Frameworks
Not applicable . WHO disease classifications do not define Westgard rules.
Laboratory Notes
- Visual flag → SOP action
- 1-2s warn; 1-3s often reject
- SOP owns the rule list
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021. (Laboratory quality and management chapters, verify current edition.)
CLSI and Professional Guidelines
- Institutional laboratory SOPs, locally adopted quality policies, and manufacturer instructions for use (IFU). Always verify current local practice.
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