A comparative study of sigma metrics and statistical quality control rules in clinical biochemistry laboratories...

The aim of this study was to use the Six Sigma metrics to assess the analytical quality of automated clinical chemistry tests in Dubai Health centers. Clinical laboratories face ongoing challenges to maintaining analytical quality, but it is difficult to measure the quality of assays objectively and quantitatively. The study assessed the quality of each analyte of general chemistry for bias, coefficient of variation (CV), sigma metrics based on the total allowable error and the applicability of Westgard rules.

Sigma metrics are an important quality planning tool for assessing total allowable error, bias, and imprecision. In this study, sigma metrics were calculated for 28 clinical chemistry analytes performed on a Roche Cobas pure analyzer. Two levels of quality control, normal and abnormal, were run daily. The coefficient of variation was calculated over a period from January to December 2024. Bias was assessed based on the laboratory results of College of American Pathologists (CAP) proficiency testing cycles and peer group comparison. Sigma metrics were calculated based on Clinical Laboratory Improvement Amendments (CLIA) total allowable error and minimum biological variation. The normalized operational specification chart assessed the applicability of the Westgard rules for the analytes.

The sigma metrics were calculated through tabulation of the two levels of internal quality controls, imprecision (CV%) and inaccuracy. The quality control rules were implemented based on the normalized operating points from the operational specifications chart.

Sigma metrics application of quality control planning tools supported the detection of false rejection and true error detection in our medical laboratories.