Application of Sigma Metrics for the Assessment and Modification of Quality Control in Clinical Chemistry Laboratory of Hospital for Tropical Diseases

Main Article Content

Vimon Yanpanich
Chatnapa Duangdee
Jittima Kunsombat


Objective: This study aims to assess the quality control performance in clinical chemistry using sigma metrics and to compare sigma metrics after quality control improvements.

Methods: This study collected %CV data from IQC and % Bias from the EQA results derived from performance evaluation using sigma metrics. The obtained data were used to identify the cause for tests with low-sigma metrics and to improve quality. All results were used to conduct comparative studies.

Results: Twenty-five tests were used to improve the quality control using the sigma metrics. It was discovered that 19 tests before the quality control improvements were included in the world class performance (≥ 6-sigma) and excellent performance (≥ 5-sigma) criteria which can be used in the rules of 13s, (N = 2, R = 1) and 13s/22s, /R4s (N =2, R=1) respectively. After quality control improvement, tests with the world class and excellent performance was increased to 22 included; glucose, creatinine, uric acid, cholesterol, triglyceride, HDL, LDL, total protein, AST, ALT, ALP, CPK, LDH, amylase, GGT, magnesium, BUN, albumin, total bilirubin, calcium, phosphorous and potassium. There was only 1 test with <4-sigma, chloride, that was applied the maximum QC 13s / 2 of 32s / R4s / 31s / 8x (N = 2, R = 4)

Conclusion: The Cobas 6000 automatic analyzer (model C501) at the Clinical Chemistry Laboratory of Tropical Medicine Hospital has an excellent diagnostic performance with a high level of six-sigma which makes it possible to choose the suitable quality control rules for testing programs. Beneficially, six-sigma provides cost saving, convenience, and easy to apply. Moreover, using sigma matric helped to reduce the clinical testing workload. However, laboratory worker must follow the all test items. In addition, the training program recognizing of six-sigma is important. Therefore, staff should have knowledge and competence to select quality control rules and interpret the control result.


Download data is not yet available.

Article Details

Original Articles


Nevalainen D, Berte L, Kraft C, Leigh E, Morgan T. Evaluating Laboratory Performance on Quality Indicators with the Six Sigma Scale. Arch Pathol Lab Med 2000; 124: 516-9.

Westgard JO, Westgard SA.The Quality of Laboratory Testing Today. An Assessment of σ Metrics for Analytic Quality Using Performance Data From Proficiency Test Surveys and the CLIA Criteria for Acceptable Performance. Am J Clin Pathol 2006; 125: 343-54.

Garber C. Six Sigma, Its Role in the Clinical Laboratory. Clinical Laboratory News 2004;11-14.

Westgard JO. Six Sigma Quality Design and Control: Desirable precision and requisite QC for laboratory measurment processes. 2nd ed. Madison WI: Westgard QC; 2006

Harry, M. J., Lawson, C. The Great Discovery: A Process That Creates Breakthrough in Everything You Do. 1st ed. Arizona: The Great Discovery, LLC Publishing; 2010

Saranpat Khaongamdechawat, Pilaiwan Siriprukpong. Efficiency of the QC Procedure Using OPSpec Chart and Sigma Metric QC Planning Tool. Med Tech Assoc Thailand 2013; 41 (2):4548-63.

Sten Westgard, Hassan Bayat , Westgard JO. Analytical Sigma metrics: A review of Six Sigma implementation tools for medical laboratories Biochem Med (Zagreb) 2018;28(2):020502.

Kanjana Kijburana. Quality Control Planning for Assessment of Clinical Chemistry Laboratory Performance, Medical Technology Department, Sawanpracharak Hospital. J Med Tech Assoc Thailand 2013: 41 (2): 4576-87.

Degandt S, Maelegheer K, Puype D, Langlois M, Vanwynsberghe T. (2015). Application of Six Sigma in a clinical chemistry core-laboratory. Advance online publication. doi:10.13140/RG.2.2.27141.14565

Mao X, Shao J, Zhang B,Wang Y. Evaluating analytical quality in clinical biochemistry laboratory using Six Sigma, Biochem Med (Zagreb) 2018;28(2): 020904.

Nanda SK, Ray L. Quantitative application of sigma metrics in medical biochemistry. J Clin Diagn Res 2013; 7(12): 2689-91.

James O Westgard, Sten A Westgard . The quality of laboratory testing today: An assessment of sigma metrics for analytic quality using performance data from proficiency testing surveys and the CLIA criteria for acceptable performance. Am J Clin Pathol 2006; 125:343–54.