Sigma metrics for assessing the analytical quality of clinical chemistry assays: a comparison of two approaches

Xiuzhi Guo,Ermu Xu,Xuehui Gao,Tingting You,Tianjiao Zhang,Fang Zhao,Ling Qiu,Xinqi Cheng,Qiong Wu,Pengchang Li,Jie Wu,Liangyu Xia

doi:10.11613/bm.2018.020708

Abstract

IntroductionTwo approaches were compared for the calculation of coefficient of variation (CV) and bias, and their effect on sigma calculation, when different allowable total error (TEa) values were used to determine the optimal method for Six Sigma quality management in the clinical laboratory.Materials and methodsSigma metrics for routine clinical chemistry tests using three systems (Beckman AU5800, Roche C8000, Siemens Dimension) were determined in June 2017 in the laboratory of Peking Union Medical College Hospital. Imprecision (CV%) and bias (bias%) were calculated for ten routine clinical chemistry tests using a proficiency testing (PT)- or an internal quality control (IQC)-based approach. Allowable total error from the Clinical Laboratory Improvement Amendments of 1988 and the Chinese Ministry of Health Clinical Laboratory Center Industry Standard (WS/T403-2012) were used with the formula: Sigma = (TEa − bias) / CV to calculate the Sigma metrics (σCLIA, σWS/T) for each assay for comparative analysis.ResultsFor the PT-based approach, eight assays on the Beckman AU5800 system, seven assays on the Roche C8000 system and six assays on the Siemens Dimension system showed σCLIA > 3. For the IQC-based approach, ten, nine and seven assays, respectively, showed σCLIA > 3. Some differences in σ were therefore observed between the two calculation methods and the different TEa values.ConclusionsBoth methods of calculating σ can be used for Six Sigma quality management. In practice, laboratories should evaluate Sigma multiple times when optimizing a quality control schedule.

Highlights

Two approaches were compared for the calculation of coefficient of variation (CV) and bias, and their effect on sigma calculation, when different allowable total error (TEa) values were used to determine the optimal method for Six Sigma quality management in the clinical laboratory
All reagents and calibrators for the three analysers were obtained from the original manufacturer except for creatinine (CREA; Maccura Biotechnology Co., Ltd., Chengdu, China) and bilirubin, total (BT; Wako Pure Chemical Industries, Ltd., Osaka, Japan) on the Beckman AU5800 system (Beckman Coulter, Inc., Brea, USA)
proficiency testing (PT) materials for routine clinical chemistry were provided by National Center for Clinical Laboratories (NCCL) (Peking, China)

Summary

Introduction

Two approaches were compared for the calculation of coefficient of variation (CV) and bias, and their effect on sigma calculation, when different allowable total error (TEa) values were used to determine the optimal method for Six Sigma quality management in the clinical laboratory. Clinical laboratory testing results are important for ensuring patient safety. Two-thirds of important clinical decisions on patient management are based on laboratory test results [1]. Continuous improvement and the minimizing of errors in testing are the major goals of every clinical laboratory. Following its introduction in clinical laboratories, 6σ quality management has become a major research focus [2]. The clinical application of 6σ quality management involves the combined use of quality requirements and laboratory performance to quantitatively evaluate whether a laboratory meets clinical testing standards.

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