Sigma Metrics: A Valuable Tool for Evaluating the Performance of Internal Quality Control in Laboratory
Background Six Sigma is a widely accepted quality management system that provides an objective assessment of analytical methods and instrumentation. Six Sigma scale typically runs from 0 to 6, with sigma value above 6 being considered adequate and 3 sigma being considered the minimal acceptable performance for a process.
Methodology Sigma metrics of 10 biochemistry parameters, namely glucose, triglycerides, high-density lipoprotein (HDL), albumin, direct bilirubin, alanine transaminase, aspartate transaminase, urea nitrogen, creatinine and uric acid, and hematology parameters such as hemoglobin (Hb), total leucocyte count (TLC), packed cell volume (PCV), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and platelet were calculated by analyzing internal quality control (IQC) data of 3 months (June–August 2019).
Results Sigma value was found to be > 6 for triglyceride, HDL, Hb, TLC, and MCH, signifying excellent results and no further modification with respect to IQC. Sigma value was between 3 and 6 for glucose, albumin, creatinine, uric acid, PCV, and MCHC, implying the requirement of improvement in quality control (QC) processes. Sigma value of < 3 was seen in AST, ALT, direct bilirubin, urea nitrogen, platelet, and MCV, signifying suboptimal performance.
Discussion Six Sigma provides a more quantitative framework for evaluating process performance with evidence for process improvement and describes how many sigmas fit within the tolerance limits.
Thus, for parameters with sigma value < 3, duplicate testing of the sample along with three QCs three times a day may be used along with stringent Westgard rules for rejecting a run.
Conclusion Sigma metrics help assess analytical methodologies and augment laboratory performance.
Artikel online veröffentlicht:
28. Juni 2021
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- 1 Adiga US, Preethika A, Swathi K. Sigma metrics in clinical chemistry laboratory—a guide to quality control. Al Ameen J Med Sci 2015; 8 (04) 281
- 2 Nanda SK, Ray L. Quantitative application of sigma metrics in medical biochemistry. J Clin Diagn Res 2013; 7 (12) 2689-2691
- 3 Mao X. et al Quality control by Six Sigma. Biochem Med (Zagreb) 2018; 28 (02) 020904
- 4 International Standards Organization (ISO), ISO 15189:2012 Medical Laboratories—Requirements for Quality and Competence. Zurich, Switzerland: International Standards Organization (ISO). 2012
- 5 Nevalainen D, Berte L, Kraft C, Leigh E, Picaso L, Morgan T. Evaluating laboratory performance on quality indicators with the six sigma scale. Arch Pathol Lab Med 2000; 124 (04) 516-519
- 6 Westgard JO. Six Sigma Quality Design and Control. 2nd ed. Madison, WI: Westgard QC Inc, 2006: 338
- 7 Coskun A, Unsal I, Serteser M, Inal T. Six Sigma as a quality management tool: evaluation of performance in laboratory medicine. www.intechopen.com. Published August 16, 2010.
- 8 Henry RJ, Segalove M. The running of standards in clinical chemistry and the use of the control chart. J Clin Pathol 1952; 5 (04) 305-311
- 9 Levey S, Jennings ER. The use of control charts in the clinical laboratory. Am J Clin Pathol 1950; 20 (11) 1059-1066
- 10 Westgard JO, Klee GG. Quality management. In: Burtis CA, Ashwood ER, Bruns DE, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. St Louis, MO: Elsevier Saunders Inc, 2006: 485-529