Background: The evaluation of pre-analytical, analytical and post-analytical phases is very important to obtain accurate, price and comparable results. Quality indicators are generally used to evaluate these processes. The present study aimed to evaluate the analytical phase using six sigma.

Material and Methods: Sigma values of 28 biochemistry tests were determined using bias, variation coefficient and total allowable error (TEa). Bias and variation coefficient were calculated external quality control and internal quality control data (IQC), respectively. TEa ratios were obtained from Clinical Laboratory Improvement Amendents (CLIA) and Ricos's biological variation values.

Results: According to TEa ratio of CLIA, in at least one internal quality control sample, sigma values were determined to be greater than 6 for ALP, ALT, amylase, CK, iron, HDL-cholesterol, magnesium, triglyceride and uric acid. When used TEa of Ricos, sigma values of ALT, amylase, total bilirubin, direct bilirubin, CK, iron, triglycerides, CRP and urea were greater than 6. However; albumin, urea and lithium had sigma value smaller than 3 according to TEa of CLIA. When used TEa of Ricos, sigma values smaller than 3 were calculated for albumin, calcium, chloride, creatinine, glucose, LDH, magnesium, total protein, sodium, total cholesterol, phosphorus and RF.

Conclusion: Even if different test parameters are being analyzed in same IQC sample on same analyzer, different sigma values might be obtained. The determination of different IQC rule for each test according to sigma values may be both improve performance and reduce IQC false rejected. Moreover, sigma values may be change according to TEa and control levels.