Curriculum
შიდა ხარისხის კონტროლი, Westgard-ის წესები და EQA [L-07]
Start here
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Course pre-test
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Part I — Internal quality control strategy
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Part II — Westgard rules
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Part III — External quality assessment
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Part IV — QC failure management
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Course post-test
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Resources
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Capstone & certificate
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Text lesson
Chapter 2 · Westgard rules
Westgard rules are decision criteria for interpreting QC data. Key rules: 1₂s warning — one result exceeds ±2SD (investigate); 1₃s rejection — one result exceeds ±3SD (reject the run); 2₂s rejection — two consecutive results exceed the same ±2SD (reject); R₄s rejection — range between two consecutive results exceeds 4SD (reject); 4₁s rejection — four consecutive results exceed the same ±1SD (reject). Running multiple QC levels increases error detection.
Chapter 2 · Practical example
Westgard rules — understanding what each rule signals
Each Westgard rule signals a different type of analytical error. Applying the right response requires understanding which rule fired and what it means.
▲ The situation
Morning QC for cholesterol shows the abnormal-level control at 3.2 SD above the mean — the 1-3s rule. Patient samples from the overnight batch are waiting. The analyst is considering re-running the same QC material.
Reference: ISO 15189:2022 Clause 7.3.7
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✓
Good practice The analyst recognises the 1-3s rule as a warning for random error. She prepares a fresh aliquot of QC material and re-runs. The fresh aliquot is within range. She investigates the original vial — it shows signs of evaporation from incomplete sealing. Root cause: inadequate QC material storage. The event is documented and patient results are released.
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✗
Poor practice The analyst re-runs the same vial until it passes. It passes on the third run. She releases patient results with no investigation and no documentation. The underlying storage issue persists. The next morning, QC again shows a 1-3s violation. The pattern of re-running until passing accumulates over weeks — eventually masking a genuine systematic error on the analyser.
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● What this means for your practice
Re-running QC from the same vial until it passes is not a QC response — it is QC avoidance. The 1-3s rule requires a fresh aliquot and an investigation. Document every QC event, including re-runs and their outcomes. The documentation is your evidence of a functioning QC system.