Postanalytical external quality assessment of blood glucose and hemoglobin A1c: an international survey.

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.