Abstract: Objective  To evaluate the performance of specific protein under different allowable total error (TEa) of different international standards, apply 6 sigma (σ) metrics into selecting and improving quality control rule.  Methods  The data from internal quality control and the proficiency test of the National Center for Clinical Laboratory in 2009 and 2010 were collected respectively, and the imprecision and bias were calculated. TEa was quoted from Clinical Laboratory Improvement Amendments 88 (CLIA′88), German Guidelines for Quality and biological variation requirements. According to the coefficient of variation (CV), bias and TEa, σ was calculated, and quality control strategy was designed. In addition, the quality goal index (QGI) below 6σ was calculated to find problem and decide the priority improvement of precision and accuracy. Results  According to IgA, IgG, IgM, C3, C4 and C reactive protein (CRP) with 3 different TEa in 2009, the σ were 0.53-6.95 respectively. The items were below 6σ except CRP, and under biological variation requirements the CRP σ was 6.95. In 2010, the σ of the 6 items was 1.33-29.39 respectively, and all items were above 6σ except IgG and C3 under biological variation requirements. Conclusions  Using the σ metric, the performance and appropriate internal quality control can be chosen and developed economically and reasonably.

Key words: Allowable total error, 6 sigma, Internal quality control