The application of 6 σtheory in assessment of the internal quality control scheme in the performance and design in Johnson Vitros 5.1 dry biochemical analyzer system

Objective To quantify the items of Johnson Vitros 5.1 dry biochemistry analysis system using 6 σtheory, and design the internal quality control (IQC) of each item, and explore the value of 6 σtheory in clinical quality management. Methods We calculated the σlevels of 8 items of Potassium, Sodium, Chlorine, Glucose, Urea, Creatinine, Cholinesterase, and Lipase in a equation of σ=[the total error (TEa) - bias] / coefficient of variation (CV). TEa was based on the external quality assessment (EQA) of National Center for Clinical Laboratory (NCCL) in 2018, with an average bias of the EQA by NCCL, and with a CV of daily imprecision from February 2016 to February 2017. According to the Westgard σrule[1], a personalized IQC scheme was developed. For items whose performance was not up to 6 σ, the quality target index (QGI=Bias/1.5CV) was calculated and the modified scheme was established. Results The σlevel of total performance of the 8 items was from 2.21 to 14.01. Among them, Cholinesterase and Lipase were above 6 σ, and Potassium, Sodium, Glucose and Creatinine were more than 3 σand less than 6 σ, while Chlorine and Urea were less than 3 σ. For items in which the performance did not reach 6 σ, when the QGI of Sodium, Urea, and Creatinine were less than 0.8, it needed to be improved in precision. When the QGI of Potassium, Chlorine, and Glucose were 0.8-1.2, it needed to be improved in both precision and accuracy. When Chlorine and Urea did not reach to 3 σ, this suggested that there were serious quality defects, for which it needed to be improved in quality improvement measures. According to the value of σ, each item of the quality control was designed individually. Conclusions The 6 σtheory can directly evaluate the performance of Johnson Vitros 5.1 dry chemical biochemistry analysis system. To design personalized IQC scheme is to guide a continuous quality improvement. Key words: Six σ; Dry chemical biochemical analyzer; Performance evaluation; Quality scheme; Quality improvement