Abstract
OBJECTIVE: Six Sigma is one of the most popular quality management system tools employed for
process improvement. The Six Sigma methods are usually applied when the outcome of
the process can be measured. This study was done to assess the performance of individual
biochemical parameters on a Sigma Scale by calculating the sigma metrics for individual
parameters and to follow the Westgard guidelines for appropriate Westgard rules and
levels of internal quality control (IQC) that needs to be processed to improve target
analyte performance based on the sigma metrics.
MATERIALS AND METHODS: This is a retrospective study, and data required for the study were extracted between
July 2015 and June 2016 from a Secondary Care Government Hospital, Chennai. The data
obtained for the study are IQC - coefficient of variation percentage and External
Quality Assurance Scheme (EQAS) - Bias% for 16 biochemical parameters.
RESULTS: For the level 1 IQC, four analytes (alkaline phosphatase, magnesium, triglyceride,
and high-density lipoprotein-cholesterol) showed an ideal performance of ≥6 sigma
level, five analytes (urea, total bilirubin, albumin, cholesterol, and potassium)
showed an average performance of <3 sigma level and for level 2 IQCs, same four analytes
of level 1 showed a performance of ≥6 sigma level, and four analytes (urea, albumin,
cholesterol, and potassium) showed an average performance of <3 sigma level. For all
analytes <6 sigma level, the quality goal index (QGI) was <0.8 indicating the area
requiring improvement to be imprecision except cholesterol whose QGI >1.2 indicated
inaccuracy.
CONCLUSION: This study shows that sigma metrics is a good quality tool to assess the analytical
performance of a clinical chemistry laboratory. Thus, sigma metric analysis provides
a benchmark for the laboratory to design a protocol for IQC, address poor assay performance,
and assess the efficiency of existing laboratory processes.
Keywords
Bias - internal quality control - quality goal index - Six Sigma - Westgard rule
