Subscribe to RSS
Sigma Metric Evaluation of Drugs in a Clinical Laboratory: Importance of Choosing Appropriate Total Allowable Error and a Troubleshooting RoadmapFinancial Support Nil.
Objectives Stringent quality control is an essential requisite of diagnostic laboratories to deliver consistent results. Measures used to assess the performance of a clinical chemistry laboratory are internal quality control and external quality assurance scheme (EQAS). However, the number of errors cannot be measured by the above but can be quantified by sigma metrics. The sigma scale varies from 0 to 6 with “6” being the ideal goal, which is calculated by using total allowable error (TEa), bias, and precision. However, there is no proper consensus for setting a TEa goal, and influence of this limiting factor during routine laboratory practice and sigma calculation has not been adequately determined. The study evaluates the impact of the choice of TEa value on sigma score derivation and also describes a detailed structured approach (followed by the study laboratory) to determine the potential causes of errors causing poor sigma score.
Materials and Methods The study was conducted at a clinical biochemistry laboratory of a central government tertiary care hospital. Internal and external quality control data were evaluated for a period of 5 months from October 2019 to February 2020. Three drugs (carbamazepine, phenytoin, and valproate) were evaluated on the sigma scale using two different TEa values to determine significant difference, if any.
Statistical Analysis Bias was calculated using the following formula: Bias% = (laboratory EQAS result − peer group mean) × 100 / peer group mean Peer group mean sigma metric was calculated using the standard equation: Sigma value = TEa − bias / coefficient of variation (CV)%.
Results Impressive sigma scores (> 3 sigma) for two out of three drugs were obtained with TEa value 25, while with TEa value 15, sigma score was distinctly dissimilar and warranted root cause analysis and corrective action plans to be implemented for both valproate and carbamazepine.
Conclusions The current study evidently recognizes that distinctly different sigma values can be obtained, depending on the TEa values selected, and using the same bias and precision values in the sigma equation. The laboratories should thereby choose appropriate TEa goals and make judicious use of sigma metric as a quality improvement tool.
21 May 2021 (online)
© 2021. The Indian Association of Laboratory Physicians. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).
Thieme Medical and Scientific Publishers Pvt. Ltd.
A-12, 2nd Floor, Sector 2, Noida-201301 UP, India
- 1 Forsman RW. Why is the laboratory an afterthought for managed care organizations?. Clin Chem 1996; 42 (05) 813-816
- 2 Bonini P, Plebani M, Ceriotti F, Rubboli F. Errors in laboratory medicine. Clin Chem 2002; 48 (05) 691-698
- 3 Bruns DE, Burtis CA. Tietz Fundamentals of Clinical Chemistry. 6th ed. Amsterdam, Elsevier 2008
- 4 Shah Goel S, Saini RB, Singh S, Aggarwal O, Goel AK. Six sigma metrics and quality control in clinical laboratory. Int J Med Res Rev 2014; 2 (02) 140-149
- 5 Westgard JO. Internal quality control: planning and implementation strategies. Ann Clin Biochem 2003; 40 (Pt 6) 593-611
- 6 Tetrault G. Evaluating laboratory performance with the six sigma scale. Arch Pathol Lab Med 2000; 124 (12) 1748-1749
- 7 Coskun A, Inal T, Unsal I, Serteser M. Six Sigma as a Quality Management Tool: Evaluation of Performance in Laboratory Medicine Quality Management and Six Sigma. Rijeka, Croatia: InTechOpen 2010: 248-261
- 8 Kumar BV, Mohan T. Sigma metrics as a tool for evaluating the performance of internal quality control in a clinical chemistry laboratory. J Lab Physicians 2018; 10 (02) 194-199
- 9 Lasky FD, Boser RB. Designing in quality through design control: a manufacturer’s perspective. Clin Chem 1997; 43 (05) 866-872
- 10 Stankovic AK, Romeo P. The role of in vitro diagnostic companies in reducing laboratory error. Clin Chem Lab Med 2007; 45 (06) 781-788
- 11 Gras JM, Philippe M. Application of the Six Sigma concept in clinical laboratories: a review. Clin Chem Lab Med 2007; 45 (06) 789-796
- 12 Llopis MA, Trujillo G, Llovet MI. et al. Quality indicators and specifications for key analytical-extranalytical processes in the clinical laboratory. Five years’ experience using the Six Sigma concept. Clin Chem Lab Med 2011; 49 (03) 463-470
- 13 Westgard JO, Westgard SA. Quality control review: implementing a scientifically based quality control system. Ann Clin Biochem 2016; 53 (Pt 1) 32-50
- 14 Hens K, Berth M, Armbruster D, Westgard S. Sigma metrics used to assess analytical quality of clinical chemistry assays: importance of the allowable total error (TEa) target. Clin Chem Lab Med 2014; 52 (07) 973-980
- 15 std. CLSI EP5–A2. Evaluation of precision performance of quantitative measurement methods; approved guideline. 2nd ed. Wayne, PA: CLSI, 2004/std
- 16 Harry M, Schroeder R. Six Sigma: The Breakthrough Strategy Revolutionizing The World’s Top Corporation. New York, NY: Random House, Doubleday 2000
- 17 Westgard JO. Quality control. How labs can apply six sigma principles to quality control planning. Clin Lab News 2006; 32: 10-12
- 18 International Organisation for Standardization. Medical Laboratories: Particular Requirements for Quality and Comp-etence. ISO 15189.Geneva: International Organization for Standardization (ISO) 2007
- 19 Westgard JO, Burnett RW. Precision requirements for cost-effective operation of analytical processes. Clin Chem 1990; 36 (09) 1629-1632
- 20 Westgard JO. Six Sigma Quality Design and Control: Desirable Precision and Requisite QC for Laboratory Measurement Processes. Madison, WI: Westgard QC 2001
- 21 Sciacovelli L, Secchiero S, Zardo L. et al. The role of the external quality assessment. Biochem Med (Zagreb) 2010; 20: 160-164
- 22 Carraro P, Plebani M. Errors in a stat laboratory: types and frequencies 10 years later. Clin Chem 2007; 53 (07) 1338-1342
- 23 Plebani M, Carraro P. Mistakes in a stat laboratory: types and frequency. Clin Chem 1997; 43 (8 Pt 1) 1348-1351