Diabetes control and complications: the role of glycated haemoglobin, 25 years on

The long‐term complications of diabetes have major consequences for individual subjects and growing healthcare delivery and cost implications for society. Evidence for the benefits of good glycaemic control, as monitored by glycated haemoglobin measurements, has been developed in the 25 years since they were introduced to the point where HbA1c assays play central roles in patient management, clinical guidance and audit, and clinical trial design. In this review this evidence is examined and three classes of uncertainty identified that diminish confidence in the effectiveness of these roles for HbA1c.