English summary: VARIATION IN RESULTS OF HBA1C DETERMINATIONS

Background

Determination of HbA_1c is a key measure of glycaemic control in follow up of diabetic patients. It is increasingly also used in evaluation of the quality in diabetes care. HbA_1c values <=7.5% in type 1 diabetes and even below 6.5% in type 2 diabetes are regarded as a measure of good diabetes care.

It is important for patients with diabetes as well as for professionals in diabetes care that the HbA_1c results of clinical laboratories are reproducible without clinically significant differences in the results provided by different laboratories. The aim of our study was to evaluate whether the results of HbA_1c measurements were comparable in two different communities.

Methods

We analyzed 35 routine venous blood samples for HbA_1c measurements taken from patients living in two communities. The blood samples were analyzed simultaneously by two different clinical laboratories using different immunological methods for HbA_1c measurement.

Results

There was a statistically highly significant correlation (0.96, p<0.001) between the HbA_1c measurements provided by the two laboratories. However, the HbA_1c levels differed significantly and consistently from each other by 0.6 percentage points (p<0.001), and the largest individual difference between the laboratories was as much as 1.6 percentage points.

Conclusions

In the clinical setting the difference found in the results of HbA_1c determinations can be considered too large and it may have an effect on clinical decision making in treatment of individual diabetic patients. The difference may also jeopardize benchmarking comparison of diabetes care between communities or diabetes care units. The comparability of the results of HbA_1c determinations still needs attention and doctors working in diabetes care should be aware of the problems in HbA_1c determinations.