Even as the world debates whether the three-month average of blood sugar (HbA1c) can be a tool to identify people at high risk of diabetes, a study from Chennai has shown that the test is highly indicative of future diabetes in Asian Indian subjects with impaired glucose tolerance (IGT).

The study by A. Ramachandran et al, published in DiabeticMedicine last week, concluded that HbA1c could show who among the pre-diabetics would go on to develop diabetes later.

Ramachandran, founder, India Diabetes Research Foundation, and A. Ramachandran's Diabetes Hospital, explains that about 55 per cent of pre-diabetics (or IGT) in the Indian population go on to develop diabetes in the next three years. “The HbA1c will tell you which of the 55 per cent will go on from pre-diabetes to diabetes.”

While the oral glucose tolerance test continues to be the gold standard for detecting diabetes, the American Diabetes Association had recently recommended HbA1c testing for the diagnosis and monitoring of diabetes, along with the existing diagnostic criteria including fasting plasma glucose, and the oral glucose tolerance test.

A total of 845 subjects were studied and their blood sugar measured over a period of three years. The blood sugar levels, including HbA1c, showed significant increase. There was also a progressive increase of diabetes with increasing levels of baseline HbA1c.

The normal value of HbA1c is 4 to 6% in subjects identified as non-diabetic. The expert panel has identified 6.5% as the A1c level for diagnosis of diabetes at which the prevalence of diabetic retinopathy begins to rise above that of non-diabetic patients, he explains.

The results showed that 50 per cent of the subjects of the study (with IGT) had a HbA1c value of over 6 per cent, 30 per cent had values between 6 and 6.5 per cent. And 20 per cent had values of over 6.5 per cent. The HbA1c turned out to be the most powerful predictors of diabetes in the three-year study period, the authors, C. Snehalatha, A. Samith Shetty, and A. Nanditha stress. Finding subjects with abnormal HbA1c appears to be valuable in identifying chronic high blood sugar. This also points out to the practitioners subjects with ‘true pre-diabetes' requiring interventions.

HbA1c is also said to be a better predictor of cardiovascular disease and other complications related to diabetes.

Among medical practitioners in the U.S., the HbA1c is seen as having advantages over the oral glucose tolerance test, which is painful (since it involves consuming a glucose solution) and time-consuming for patients, he says. Besides, the time spent at a hospital for the GTT is seen as having an impact on indirect costs for the patients.

The HbA1c on the other hand requires only blood from the vein, and takes lesser time. However, laboratory tests can be expensive and the measurement of HbA1c is not standardised, like many other values, in Indian labs, Dr. Ramachandran points out.