Aim: Six Sigma is a quality management tool that helps continuously monitor and improve the performance of the tests in the clinical laboratory. The quality goal index (QGI) ratio represents the state of meeting the respective quality targets of both bias and precision. The aim of the present study was to calculate sigma metrics and QGI for several complete blood count tests, using ESFEQA (European Society for External Quality Assessment) TEA requirements.

Materials and Methods: This retrospective study was conducted in Marmara University Pendik E&R Hospital Biochemistry Laboratory Hematology Unit. The %bias, %CV, and total allowable error (TEa) of the tests were used in sigma and QGI calculations accordingly, sigma=(TEa−bias)/CV and QGI=bias/1.5 CV

Results: The performance of each test was evaluated with Sigma metrics and QGI. WBC (all levels), RBC (level 3), hemoglobin (level 2), hematocrit (levels 2 and 3), and MCV (levels 2 and 3) showed an ideal performance with>6 sigmas. RBC and hemoglobin showed medium implementation of ≥3-<4 sigma for the first quality control level. For all analytes with sigma <5, QGI was <0.8 indicating imprecision errors (RBC level 1 and 2, Hb level 1) while a QGI ratio of >1.2 indicated inaccuracy problems (PLT level 1). QGI value between 0.8 and 1.2 calculated for the 1st level quality control samples for the hematocrit test was interpreted as both precision and accuracy error.

Conclusion: This study shows that sigma metrics and QGI ratio is good quality tools to evaluate the analytical performance of a hematology laboratory.