Practical application of Sigma Metrics QC procedures in clinical chemistry

Clin Chem Lab Med. 2011 Nov;49(11):1837-43. doi: 10.1515/CCLM.2011.249. Epub 2011 Jul 29.


Background: Many labs have not yet selected the most appropriate Westgard Quality Control (QC) rule for each test. This is mainly due to the apparent complexity of the matter.

Methods: From the Westgard OPSpecs Charts QC planning tool and the Sigma Metrics formula's it was deduced that every Westgard rule has its own Sigma value. This was converted to an easy three-step road map to optimal Westgard QC rules.

Results: The road map provided is based on Sigma Metrics that hold a definition of "world class quality", at which no further effort to increase quality needs to be taken. Furthermore, it is shown that clinical chemical tests can be classified as "good": quality at or above world class, "bad": quality below world class but controllable with Westgard QC rules and "ugly": quality not controllable with Westgard QC rules alone. Finally, practical tips of how to deal with this and related aspects are given.

Conclusions: The use of the road map based on Sigma Metrics leads to fast and easy implementation of optimal Westgard QC rules.

MeSH terms

  • Biomarkers* / blood
  • Biomarkers* / urine
  • Chemistry, Clinical / methods*
  • Data Interpretation, Statistical*
  • Humans
  • Laboratories / standards*
  • Quality Control
  • Software*
  • Validation Studies as Topic


  • Biomarkers