Committee recommends HbA1c assay to diagnose diabetes

American Diabetes Association's 69th Scientific Sessions

The HbA1c assay should be the new method for diagnosing diabetes in adults and children, an international expert committee recommended on Friday.

The two methods currently used to diagnose diabetes are fasting plasma glucose or oral glucose tolerance tests.

“After reviewing lots of clinical chemistry data, we determined that there are numerous advantages of HbA1c over glucose,” committee chair David M. Nathan, MD, said during a press conference.

The International Expert Committee, with members appointed by the American Diabetes Association, European Association for the Study of Diabetes and International Diabetes Federation, reported the proposed recommendations during a symposium here.

The committee has established an HbA1c cut point of ≥6.5% for the diagnosis of diabetes. Further, a level ≥6% but <6.5% is sufficient to identify individuals at especially high risk for diabetes, the committee said.

However, Nathan cautioned that the cut point of 6.5% should not be construed as an “absolute dividing line” between normal glycemia and diabetes because “glucose impairment runs on a continuum.”

“This is the first major departure from the way we’ve been diagnosing diabetes for more than 30 years, using a lab tool that reflects chronic glycemia and is slightly different than the acute measurement of glucose, which has been used traditionally,” said Nathan, director of the Diabetes Center at Massachusetts General Hospital, Boston.

Advantages of HbA1c

The proposed recommendations are based on the relationship between long-term glycemic exposure and complications. Review of currently published data suggests that a reliable measure of chronic glycemic levels, such as HbA1c — which measures average blood glucose over a period of two to three months — may serve as a better marker and diagnostic test for diabetes than FPG or OGTT.

“HbA1c values vary less than FPG values and the assay for HbA1c has technical advantages compared with the glucose assay. Also, testing for diabetes using HbA1c is more convenient and easier for patients who will no longer be required to perform a fasting or OGTT,” Nathan said.

The recommendations extend only to non-pregnant adults and children.

“Information indicates that physicians are already using HbA1c on their own, a self-decided cut point for what is the diagnosis of diabetes. It’s hard to predict the future but I don’t think this is something that is going to take years and years” to implement, committee member Richard Kahn, PhD, Chief Medical and Scientific Officer of the ADA, said during the press conference.

The recommendations will be referred to working groups and practice committees before an official statement is issued by the aforementioned organizations.

The report was published ahead of print and will appear in the July issue of Diabetes Care. – by Katie Kalvaitis

[The ADA] supports the conclusions of the paper that basically says that the HbA1c measurement is appropriate for diagnosing diabetes. Right now, our focus is on what comes next. There are implications every time a parameter is chosen and changed. There are human complications, what does this mean for people with diabetes? We have to figure that out. The best way we can do that is to now refer this to our practice group who will review the papers and give us a report on what they think the implications are…the medical implications, financial implications, worldwide implications of changing the primary criteria for the diagnosis of diabetes.

– R. Paul Robertson, MD

President, Medicine and Science, ADA

HbA1c is a reasonable measure of glucose and, therefore, HbA1c is going to be a reasonable measure of glucose in people with lower blood sugar, with intermediate blood sugar and with higher blood sugar. The fact is, in the real world of clinical care, people have multiple conditions so the use of the HbA1c is a very useful test. I use it all the time, every day. But I try to be cognoscente of the fact that what I am really interested in is the blood glucose; I am interested in HbA1c to the extent that it is a representative of blood sugar. The reality is that having HbA1c be a therapeutic goal is, in a very real sense, a tremendous implication.

Dr. Nathan pointed out that HbA1c may have a few advantages over glucose, being that it is less variable and there is a lower likelihood of deterioration in the sample after taking the blood - which is a valid point. If you take blood and it doesn't get to the lab for one day, the blood sugar will be 0 whereas the HbA1c percentage would be unchanged. However, I am not sure how much of a real factor that is. Dr. Nathan showed evidence that there is a 2% analytic variability with glucose vs. 0.6% with HbA1c in optimal lab conditions. There is a great deal of evidence that HbA1c is also somewhat variable in the real world.

The most important problem, which was not really addressed, is that HbA1c is a rough indicator of mean glycemia for the majority of patients; but for a substantial majority, about 20% of patients, the HbA1c grossly underestimates or grossly overestimates the mean blood sugar. There are very good data from the Diabetes Prevention Program and NHANES that suggest that blacks have an HbA1c about 0.4% to 0.5% higher than whites. Now, that means that HbA1c goes out the window for a population of persons of varying ethnicity. Also, there is very good evidence from the Framingham Heart Study and NHANES that HbA1c increases with age, independent of changes in glycemia. One study reported that the HbA1c of a patient older than 70 years is about 0.4% higher than a patient who is 40. This means that HbA1c also goes out the window for the diagnosis of prediabetes in people as they get older.

– Zachary T. Bloomgarden, MD

Endocrine Today Editorial Board member