The development of a true reference measurement system by the International Federation for Clinical Chemistry (IFCC) for the first time allows reporting of true HbA1c results, standardized to an absolute value, worldwide. Regression equations between the IFCC assay and current harmonization assays, including the Diabetes Control and Complications Trial (DCCT) assay, are linear, tight, and stable over time. National and international setting of targets, audit and benchmarking of services will be easier than before, as will translation of research into clinical practice. Nevertheless, the main disadvantage of the IFCC assay is that the numbers and units reported (mmol/mol) are very different from the DCCT value (percentage). An extensive education program for patients and health-care professionals is, therefore, needed to prevent confusion and consequent deterioration in glycemic control. Furthermore, the IFCC system does not overcome difficulties inherent in the measurement and interpretation of HbA1c, such as in the presence of abnormal turnover of red blood cells and hemoglobinopathies.