Glycated haemoglobin for diagnosing diabetes

International Expert Committee Report on the Role of the A1C Assay in the Diagnosis of Diabetes. Diabetes Care 2009; 32(7):1327-1334

Not a new idea, but expert committees in the past have argued against the use of HbA1c for diagnosing diabetes because of lack of standardisation of the assays. However, advances in laboratory methods and standardisation have resulted in precision and accuracy of modern A1c assays comparable to that of glucose assays. The current expert committee comprising representatives from the ADA, the EASD and the IDF has proposed an HbA1c >/= 6.5% for the diagnosis of diabetes.

Recommendation of the International Expert Committee

For the diagnosis of diabetes:

• The A1C assay is an accurate, precise measure of chronic glycemic levels and correlates well with the risk of diabetes complications.
• The A1C assay has several advantages over laboratory measures of glucose.
• Diabetes should be diagnosed when A1C is >/= 6.5%. Diagnosis should be confirmed with a repeat A1C test. Confirmation is not required in symptomatic subjects with plasma glucose levels > 200 mg/dl (>11.1 mmol/l).
• If A1C testing is not possible, previously recommended diagnostic methods (e.g., FPG or 2HPG, with confirmation) are acceptable.
• A1C testing is indicated in children in whom diabetes is suspected but the classic symptoms and a casual plasma glucose > 200 mg/dl (> 11.1 mmol/l) are not found.

For the identification of those at high risk for diabetes:

• The risk for diabetes based on levels of glycemia is a continuum; therefore, there is no lower glycemic threshold at which risk clearly begins.
• The categorical clinical states pre-diabetes, IFG, and IGT fail to capture the continuum of risk and will be phased out of use as A1C measurements replace glucose measurements.
• As for the diagnosis of diabetes, the A1C assay has several advantages over laboratory measures of glucose in identifying individuals at high risk for developing diabetes.
• Those with A1C levels below the threshold for diabetes but >/= 6.0% should receive demonstrably effective preventive interventions. Those with A1C below this range may still be at risk and, depending on the presence of other diabetes risk factors, may also benefit from prevention efforts.
• The A1C level at which population-based prevention services begin should be based on the nature of the intervention, the resources available, and the size of the affected population.