Quality Control Procedures, Documentation and Interpretation: Westgard Rules

Westgard Rule 13S

  • Westgard rule 13s states that if a control is greater than ± 3 standard deviations from the mean, it should be rejected and rerun.
  • This is because either a random error or a very large systematic error has occurred, as less than 1% of all test values exceed ± 3SD.
  • In the accompanying example, the control for Day 13(noted by the arrow) is greater than +3SD from the mean. Consequently rule 13s applies and the run is rejected. Troubleshooting must be performed before further testing can be done.

Provide cost-effective continuing education and laboratory safety training to your laboratory employees. Learn more.

Quality Control course details »

Learn more about medical technologist continuing education for MTs, MLTs, and other lab personnel »

Get information on laboratory safety training for clinical and medical laboratories »