Background: Hemoglobin A1c, (HbA1c) which is the major constituent of glycated hemoglobin, has been used in the follow-up of retrospective glycemia for years and in the diagnosis of diabetes mellitus nowadays. Since the analytical performance of HbA1c should be high likewise all laboratory tests, various quality control measures are used. Sigma metrics is one of these measures and it is the combination of bias, precision and total allowable error that ensures a general evaluation of analytical quality. The aim of our study was to evaluate the analytical performance of Bio-Rad’s Variant Turbo II HbA1c analyzer according to sigma metrics.
Methods: Sigma levels were calculated using the data obtained from two levels of internal and 12 external quality control materials (Bio-Rad) of Variant II Turbo HbA1c analyzer according to s= (TEa% - Bias%) / CV% formula.
Results: The mean sigma levels for low and high quality control materials were found to be 3.0 and 4.1, respectively.
Conclusions: The annual mean analytical performance of Variant II Turbo HbA1c analyzer was found to be acceptable according to sigma metrics. In order to be sure of the difference in HbA1c results indicating the success or failure in treatment but not arise from analytical variation, it is thought that more stringent quality control measures should be applied to reach higher sigma levels.
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1. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care 2010; 33: S11–S61.
2. International Expert Committee. International expert committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care 2009; 32: 1327–34.
3. White NH Sun W Cleary PA Tamborlane WV Danis RP Hainsworth DP et al. Effect of prior intensive therapy in type 1 diabetes on 10-year progression of retinopathy in the DCCT/EDIC: comparison of adults and adolescents. Diabetes 2010; 59: 1244–53.
4. John G English E. IFCC standardized HbA1c: should the world be as one? Clin Chem Lab Med 2012; 50: 1243–8.
5. Weykamp C John WG Mosca A. A review of the challenge in measuring hemoglobin A1c. J Diabetes Sci Technol 2009; 3: 439–45.
6. Little RR Rohlfing CL Sacks DB. Status of hemoglobin A1c measurement and goals for improvement: from chaos to order for improving diabetes care. Clin Chem 2011; 57: 205–14.
7. Little RR Rohlfing CL. The long and winding road to optimal HbA1c measurement. Clinica Chimica Acta 2013; 418: 63–71.
8. Weykamp C. HbA1c: a review of analytical and clinical aspects. Ann Lab Med 2013; 33: 393–400.
9. Sacks DB Arnold M Bakris GL Bruns DE Horvath AR Kirkman MS et al. Executive summary: guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem 2011; 57: 793–8.
10. Milenković N Ignjatović S Šumarac Z Majkić-Singh N. Uncertainty of measurement im laboratory medicine. J Med Biochem 2018 37: 279–88.
11. Westgard JO Westgard SA. 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.
12. Nar R Emekli ID. The evaluation of analytical performance of immunoassay tests by using six-sigma method Nar R Emekli DI. J Med Biochem 2017; 36: 301–8.
13. Woodworth A Korpi-Steiner N Miller JJ Rao LV Yundt-Pacheco J Kuchipudi L et al. Utilization of assay performance characteristics to estimate hemoglobin A1c result reliability. Clin Chem 2014; 60: 1073–9.
14. Weykamp C John G Gillery P English E Ji L Lenters-Westra E et al. Investigation of 2 models to set and evaluate quality targets for HbA1c: biological variation and sigma-metrics. Clin Chem 2015; 61: 752–9.
15. Westgard JO Westgard SA. Assessing quality on the sigma scale from proficiency testing and external quality assessment surveys. Clin Chem Lab Med 2015; 53: 1531–5.
16. Lenters-Westra E English E. Understanding the use of sigma metrics in hemoglobin A1c analysis. Clin Lab Med 2017; 37: 57–71.
17. Zhao HJ Zhang TJ Zeng J Hu CH Ma R Zhang CB. Investigation and analysis of HbA1c measurement systems’ performance for 135 laboratories in China. Chin Med J 2017; 130: 1079–84.
18. Huysal K Budak YU. Application of sigma metrics for the assessment of quality assurance using the MQ-2000 PT HbA1c analyzer. Biochem Med 2015; 25: 416–20.
19. Braga F Dolci A Montagnana M Pagani F Paleari GC Guidi GC et al. Revaluation of biological variability of glycated haemoglobin using an accurately designed protocol and assay traceable to the IFCC reference system. Clin Chim Acta 2011; 412: 1412–6.
20. Goodall I Colman PG Schneider HG McLean M Barker G. Desirable performance standards for HbA1c analysis– precision accuracy and standardization: Consensus statement of the Australian Association of Clinical Biochemists (AACB) the Australian Diabetes Society (ADS) the Royal College of Pathologists of Australia (RCPA Endocrine Society of Australia (ESA) and the Australian Diabetes Educators Association (ADEA). Clin Chem Lab Med 2007; 45: 1083–97.