Abstract
HbA1c is a key parameter in diabetes management. For years the test has been used exclusively for monitoring of long-term diabetic control. However, due to improvement of the performance, HbA1c is considered more and more for diagnosis and screening. With this new application, quality demands further increase. A task force of the International Federation of Clinical Chemistry and Laboratory Medicine developed a model to set and evaluate quality targets for HbA1c. The model is based on the concept of total error and takes into account the major sources of analytical errors in the medical laboratory: bias and imprecision. Performance criteria are derived from sigma-metrics and biological variation. This review shows 2 examples of the application of the model: at the level of single laboratories, and at the level of a group of laboratories. In the first example data of 125 individual laboratories of a recent external quality assessment program in the Netherlands are evaluated. Differences between laboratories as well as their relation to method principles are shown. The second example uses recent and 3-year-old data of the proficiency test of the College of American Pathologists. The differences in performance between 26 manufacturer-related groups of laboratories are shown. Over time these differences are quite consistent although some manufacturers improved substantially either by better standardization or by replacing a test. The IFCC model serves all who are involved in HbA1c testing in the ongoing process of better performance and better patient care.