Citation Information :
Mahavadi S, Shanthakumari J. Effect of Matrix and Source of Quality Specification Data on the Sigma Metrics of Common Chemistry Analytes in Clinical Laboratory. Indian J Med Biochem 2022; 26 (1):1-8.
Introduction and aim: Internal and external quality control (IQC and EQC) is used to monitor and evaluate the analytical process. Six Sigma provides an objective assessment of performance. The Sigma metrics (σ) are calculated using the coefficient of variation (CV), bias, and total allowable error (TEa). One of the pitfalls of the Sigma metrics calculation is that it depends upon the source of the variables used in the formula and the measurand matrix. Hence, this study was conducted to calculate the Sigma metrics of urea, creatinine, Na, and K in serum and urine using Tea from biological variation (BV) (urine and serum) and Clinical Laboratory Improvement Amendments (CLIA) (serum) and subsequently comparing the Sigma metrics of all four analytes using TEa from BV between serum and urine control and using TEa from BV in the same matrix (serum). Materials and methods: A cross-sectional study was conducted in the Department of Clinical Biochemistry, St. John's Medical College for 1 year (January–December 2018). Bio-Rad IQC (serum and urine) data have been used to calculate σ of urea, creatinine, Na, and K. The cumulative CV and bias were obtained using unity real-time software from Bio-Rad Laboratories. Total allowable error values were obtained from BV and CLIA guidelines. Results: Urea, creatinine, Na, and K showed higher σ in the urine control than in serum controls indicating the better performance of these parameters in the urine matrix than in serum. In the same matrix (serum control), creatinine, Na, and K had higher σ using TEa from CLIA than TEa from BV. Na showed the highest difference in σ value between the two sources (p-value < 0.001). However, serum urea showed higher σ using TEa from BV compared to TEa from CLIA. Conclusion: Our study showed that σ varies with the matrix; henceforth, one should be careful in extrapolating the performance characteristics in terms of Sigma of an analyte from one matrix to another. In the same matrix, σ also varies depending on the source of TEa used in the calculation. It is, thus, essential to mention the source of the variables used to calculate σ for a better interpretation.
Adiga U, Preethika A. Sigma metrics of electrolytes – A pilot study. Int J Res Stud Biosci 2015;3:33–37, ISSN 2349-0365.
Coskun A, Unsal I, Serteser M, et al. Six sigma as a quality management tool: evaluation of performance in laboratory medicine. In: Coskun A, ed. Quality Management and Six Sigma. Sciyo 2010. Available from: http://www.intechopen.com/books/quality-management-and-six-Sigma/six-Sigma-as-a-quality-management-tool-evaluation-of-performance-in-laboratory-medicine. Accessed on: 27 August 2019.
Lakshman M, Reddy BR, Bhulaxmi P, et al. Evaluation of sigma metrics in a medical biochemistry lab. Int J Biomed Res 2015;6(3):164. DOI: https://doi.org/10.7439/ijbr.v6i3.1709.
Hens K, Berth M, Armbruster D, et al. 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(7): 973–980. DOI: https://doi.org/10.1515/cclm-2013-1090.
Afrifa J, Gyekye S, Owiredu W, et al. Application of sigma metrics for the assessment of quality control in clinical chemistry laboratory in Ghana: A pilot study. Niger Med J 2015;56(1):54–58. DOI: 10.4103/0300-1652.149172.
Gami B, Patel D, Chauhan K, et al. Sigma metrics as a quality marker for analyzing electrolytes in laboratory. Int J Adv Res 2013;1(7):197–201. ISSN: 2320-5407.
Singh B, Goswami B, Gupta VK, et al. Application of sigma metrics for the assessment of quality assurance in clinical biochemistry laboratory in India: A pilot study. Indian J Clin Biochem 2011;26(2): 131–135. doi: 10.1007/s12291-010-0083-1.
SixSigmaPreview.pdf. https://www.westgard.com/lesson67.htm. Accessed on 29 August 2019.
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(2):194–199. DOI: 10.4103/JLP.JLP_102_17.
Sciacovelli L, Secchiero S, Zardo L, et al. The role of the external quality assessment. Biochem Med 201020(2);160–164. DOI: 10.11613/BM.2010.019.
Westgard JO. Six Sigma Quality Design and Control. https://www.westgard.com/lesson67.htm Accessed on 29 August 2019.
Pyzdek T, Keller PA. Six Sigma Handbook: A Complete Guide for Green Belts, Black Belts, and Managers at All Levels, Third Edition (McGraw-Hill: New York, Chicago, San Francisco, Lisbon, London, Madrid, Mexico City, Milan, New Delhi, San Juan, Seoul, Singapore, Sydney, Toronto, 2010). ISBN: 9780071623384.
Deming WE. Quality, productivity and competitive Position, Vol. 2, Quality and Reliability Engineering International. 1982, p. 373.
Keller PA. The Six Sigma Handbook. https://www.mtcbh.net/mt-content/uploads/2017/01/6-sigma-handnbook.pdf (Accessed on 28th August 2019).
Longden H. Lean Six Sigma in Pharmaceutical QC Laboratories, 2011. https://www.academia.edu/20639566/Lean_Six_Sigma_in_Lean_Six_Sigma_in_Pharmaceutical_QC_Laboratories. Accessed on 30october 2019.
Westgard's basic QC practices.pdf. https://www.westgard.com/basic-qc-practices-4th-ed.htm. (Accessed on 25th October 2019).
Guide R, Qc E, Management D. Reference guide for expert QC data management, March 8, 2009. Time 2009 (Accessed on: 14 October 2019). https://unityweb.qcnet.com/Documentation/Help/URTO/2683.htm.
Friedecky B, Kratochvila J, Budina M. Why do different EQA schemes have apparently different limits of acceptability. Clin Chem Lab Med 2011;49(4):743–745. https://doi.org/10.1515/CCLM.2011.105.
Xia J, Chen S, Xu F, et al. Quality specifications of routine clinical chemistry methods based on sigma metrics in performance evaluation. J Clin Lab Anal 2018;32(3):e22284. https://doi.org/10.1002/jcla.22284.
Westgard J. Consolidated comparison of chemistry performance specifications. Available from https://www.westgard.com/consolidated-goals-chemistry.htm (Accessed on 11 November 2019).
Burtis CA, Ashwood ER, Bruns DE, et al. Tietz fundamentals of clinical chemistry, 6th ed., St. Louis, Mo: Saunders/Elsevier; 2008, p. 952.
Guo X, Zhang T, Gao X, et al. Sigma metrics for assessing the analytical quality of clinical chemistry assays: a comparison of two approaches. Biochem Med 2018;28(2):020708. DOI: 10.11613/BM.2018.020708.
Westgard J. 2019: CLIA proposed changes to PT acceptable limits. Available from https://www.westgard.com/2019-clia-changes.htm (Accessed on: 25 October 2019).
Westgard J. Desirable biological variation database specifications. Available from https://www.westgard.com/biodatabase1.htm (Accessed on: 11 November 2019).
Sun YC, Li Y, Tong J, et al. An interdisciplinary approach to treat crown root fractured tooth. Niger Med J 2013;54(4):274–277. DOI: 10.4103/0300-1652.119664.