Quality Control Procedures, Documentation and Interpretation: Westgard Rules

Westgard Rule 22S

  • Westgard rule 22s states that if two or more controls are greater than ± 2 standard deviations from the mean on the same day of testing or if the same control is greater than + 2 standard deviations on two consecutive measurements then the run must be rejected.
  • If this circumstance occurs, a systematic error is likely.
  • The top chart represents the day's "normal" control, while the bottom chart shows the day's "elevated" control.
  • The L-J plots on the 13th day for both the normal and elevated controls show greater than +2SD. Troubleshooting must be performed before testing can continue.
  • Had only one of the controls been greater than ± 2SD, the run would have been accepted as “in control”.

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