Impact of haemoglobin variants on the use of haemoglobin A1c for the diagnosis and monitoring of diabetes: a contextualised review.

HbA1c is the established test for monitoring glycaemic control in diabetes, and intervention trials studying the impact of treatment on glycaemic control and risk of complications focus predominantly on this parameter in terms of evaluating the glycaemic outcomes. It is also the main parameter used when targets for control are being individualised, and more recently, it has been used for the diagnosis of type 2 diabetes. For laboratories performing this test and clinicians utilising it in their decision-making process, a thorough understanding of factors that can impact on the accuracy, and appropriate interpretation of the test is essential. The changing demographic in the Irish population over the last two decades has brought this issue sharply into focus. It is therefore timely to review the utility, performance and interpretation of the HbA1c test to highlight factors impacting on the results, specifically the impact of haemoglobin variants, and the impact of these factors on its utilisation in clinical practice.