A retrospective study to evaluate the performance of internal quality control in a biochemistry laboratory using sigma metrics

Abstract

To evaluate the performance of internal quality control in a biochemistry laboratory using Sigma metrics. Data were extracted from December 2018 to November 2019 from a Tertiary care hospital, Coimbatore. The data regarding internal quality control (IQC) and external quality assurance scheme (EQAS) were collected for 14 biochemical parameters. Sigma metrics were calculated using total allowable error (TEa), Coefficient of variance (CV) and percent bias for the above mentioned parameters. Quality goal index (QGI) ratio was used to analyze the reason for the lower sigma in analytes.Coefficient of variance (CV) from the calculated laboratory means and calculated standard deviation. Sigma metrics was calculated from CV%, TEa and Bias. Quality goal index ratio was calculated from CV% and Bias.In this study four parameters AST, ALP, Triglycerides and Amylase with sigma values >6; Six parameters Total Protein, ALT, HDL, Glucose, Calcium and Cholesterol with sigma values 3 to 6 and four parameters Albumin, Uric acid, Creatinine, and Urea with sigma values <3. For all analytes <6 sigma level, the quality goal index (QGI) was <0.8 indicating the parameters which needed improvement in imprecision, except for total protein and cholesterol whose QGI >1.2 indicated inaccuracy.In the present study Sigma value was highest for ALP (7.81) and lowest for Urea (1.27). Use of alternative methods can be done for the parameters whose sigma values less than 3 to improve their performance are recommended.