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HbA1c for diabetes diagnosis?

The British Medical Journal has published an analysis of the recent expert committee recommendation that HbA1c be adopted for use in diagnosing type 2 diabetes.

The expert committee included members appointed by the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation. They concluded that anyone with a confirmed HbA1c greater than or equal to 6.5% (48mmol/mol) should be diagnosed as being type 2 diabetic in the absence of a glucose test.

This article goes on to discuss the advantages and disadvantages of using HbA1c. Advantages include a lesser day-to-day in-person variability in HbA1c compared to fasting glucose and the non-fasting state of the HbA1c blood test. Disadvantages include the complications introduced by blood disorders like sickle cell or iron deficiency anaemia and the effect of age and ethnicity. HbA1c is 0.4% higher in those aged over 70 compared to those aged 40 with the same glucose tolerance. A similar variability applies when comparing ethnic groups, for example HbA1c is 0.4% higher in Afro-Caribbeans compared with Europids.

The authors of this article conclude that, measuring glucose may present less of a risk of complete misdiagnosis than measuring HbA1c alone. They further state that, a move to HbA1c only diagnosis could be a step too far.

Action: Clinicians should continue to use the current WHO diagnostic criteria (PDF) for screening and diagnosing type 2 diabetes.