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Postanalytical External Quality Assessment of Blood Glucose and Hemoglobin A_1c: An International Survey

¹ NOKLUS, Norwegian Centre for Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway.
² Laboratori Clínic Bon Pastor Barcelona and the Analytical Quality Commission of the Spanish Society of Clinical Biochemistry and Molecular Pathology (SEQC), Barcelona, Spain.
³ Department of Clinical Chemistry, University of Szeged, Albert Szent-Gyorgyi Medical and Pharmaceutical Centre, Szeged, Hungary.
⁴ Department of Clinical Chemistry, St. Elisabeth Hospital, Tilburg, The Netherlands.
⁵ The Department of General Practice, The University of Adelaide, Adelaide, Australia.
⁶ EQUALIS AB, Uppsala, Sweden.
⁷ Faculty of Natural Sciences, University of Pretoria, Pretoria, South Africa.

^aAddress correspondence to this author at: Department of Medicine, Stavanger University Hospital, PO Box 8100, 4068 Stavanger, Norway. Fax 47-51-519-9-06; e-mail svskeie{at}online.no.

Background: Diabetes mellitus (DM) is diagnosed and monitored worldwide by blood glucose (BG) and glycohemoglobin A_1c (HbA_1c) testing, respectively. Methods for quality assessment of clinician interpretations of changes in these laboratory results have been developed. This study uses survey responses from general practitioners (GPs) in different countries to investigate possible differences in interpretation of results, as well as the feasibility of performing international postanalytical external quality assessment surveys (P-EQAS).

Methods: GPs recruited from 7 countries received questionnaires requesting interpretation of changes in a potentially diagnostic capillary BG result and an HbA_1c value obtained during monitoring of a patient with type 2 DM. GPs were asked to estimate clinically significant differences between 2 consecutive laboratory results [critical difference (CD)/reference change value] for both BG and HbA_1c. The CDs reported by GPs were used to calculate the analytical variation (CV_a), which was taken as the quality specification for analytical imprecision. Participants received national benchmarking feedback reports after the survey.

Results: The study included responses from 2538 GPs. CDs in BG results showed the same pattern and were comparable among countries. Calculated median CV_a values would be possible to attain at 80% confidence but not at the conventional 95% confidence. For HbA_1c, the same pattern was shown across countries, but with lower changes considered true when HbA_1c increased than when it decreased. Despite the consistent pattern, variations among GPs were considerable in all countries.

Conclusions: Assessments of CDs for BG and HbA_1c were similar internationally, and quality specifications for these analytes based on clinicians’ opinions are therefore interchangeable among countries. International P-EQAS may contribute to a more rational use of laboratory services and clinical guidelines.

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