Lab Med Online.  2021 Jan;11(1):11-16. 10.47429/lmo.2021.11.1.11.

Evaluating the Performance of an Automated Chemistry Analyzer Using Sigma Metrics

• Kim Sw
• Cho Y
• Yun SG

• KMID: 2525775
• DOI: http://doi.org/10.47429/lmo.2021.11.1.11

Abstract

Background
Quality control (QC) is important for producing reliable test results in the clinical laboratory. Sigma metrics is used to evaluate the performance of laboratory instruments. It calculates the sigma value and determines the number of quality control material and strategy for the internal QC of the laboratory according to the sigma value.
Methods
This study was conducted in the clinical laboratory of Korea University Anam Hospital for 6 months. We evaluated internal quality control data of 37 analytes on the automated chemistry analyzer. By Sigma metrics, we calculated the sigma value by (TEa-bias%)/coefficient of variance.
Results
The analytes that exceeded the 6 sigma value were haptoglobin, ALP , AST High level, ALT, amylase, direct & total bilirubin, CK, Fe, Mg High level, GGT, lipase, LD, HDL-cholesterol High level, protein High level, triglyceride, TIBC High level, ferritin High level, and uric acid. IgA, RF High level, protein Low level, and TIBC Low level showed 5–6 Sigma values. RF Low level, AST Low level, creatinine, Cl, K, Na, Mg Low level, glucose, HDL-cholesterol Low level, and ferritin Low level showed 3–5 sigma values. Sigma values below 3 at both Low and High level QC materials were Ca, LDL-cholesterol, total cholesterol, BUN, and total CO 2.
Conclusions
In clinical laboratories, sigma metrics should be used as a basis for adopting different Westgard rules for each test and for efficient quality control operations. Also, in the case of analytes with sigma values below 3, improvement in the overall test process is needed.

Keyword

Sigma metrics; Westgard rule; Bias; Quality control

Reference

1. Korean Society for Laboratory Medicine. 2014. Laboratory Medicine. 5th ed. Panmuneducation;Seoul:

2. Hens K, Berth M, Armbruster D, Westgard S. 2014; Sigma metrics used to assess analytical quality of clinical chemistry assays: importance of the allowable total error (TEa) target. Clin Chem Lab Med. 52:973–80. DOI: 10.1515/cclm-2013-1090. PMID: 24615486.

3. Mao X, Shao J, Zhang B, Wang Y. 2018; Evaluating analytical quality in clinical biochemistry laboratory using Six Sigma. Biochem Med (Zagreb). 28:20904. DOI: 10.11613/BM.2018.020904. PMID: 30022890. PMCID: PMC6039163.

4. Singh B, Goswami B, Gupta VK, Chawla R, Mallika V. 2011; Application of sigma metrics for the assessment of quality assurance in clinical biochemistry laboratory in India: a pilot study. Indian J Clin Biochem. 26:131–5. DOI: 10.1007/s12291-010-0083-1. PMID: 22468038. PMCID: PMC3107403.

5. Westgard QC. Desirable biological variation database specifications. https://www.westgard.com/biodatabase1.htm. Update on 2014.

6.  AAB Proÿciency Testing. AAB 2020 Program Guide. https://www.aab-pts.org/2020programguide/. Updated on Jan, 2020.

7. Westgard QC. Introducing Westgard Sigma Rules. https://www.westgard.com/westgard-sigma-rules.htm. Update on Sep, 2014.

8. Westgard JO. 2014. Basic quality management systems: essentials for analytical quality assurance. Westgard QC;WI:

9. Adiga US, Preethika A, Swathi K. 2015; Sigma metrics in clinical chemistry laboratory-A guide to quality control. Al Ameen J Med Sci. 8:281–7.

10. El Sharkawy R, Westgard S, Awad AM, Ahmed AOI, Iman EH, Gaballah A, et al. 2018; Comparison between Sigma metrics in four accredited Egyptian medical laboratories in some biochemical tests: an initiative towards sigma calculation harmonization. Biochem Med (Zagreb). 28:20711. DOI: 10.11613/BM.2018.020711. PMID: 30022886. PMCID: PMC6039160.

11. Kumar BV and Mohan T. 2018; Sigma metrics as a tool for evaluating the performance of internal quality control in a clinical chemistry laboratory. J Lab Physicians. 10:194–9. DOI: 10.4103/JLP.JLP_102_17. PMID: 29692587. PMCID: PMC5896188.

12. Chung HJ, Lee W, Chun S, Kang SY, Lee WI, Park HI, et al. 2009; Changes in total CO₂ measurement according to reagent cassette rotation in chemistry autoanalyzers. Ann Clin Lab Sci. 39:150–4.

13. Westgard S, Westgard QC. Quantitating quality: best practices for estimating the sigma-metric. https://pdfs.semanticscholar.org/9ee9/53e708a646dfa274b481e4629e6391c842e1.pdf. Updated on 2016.