SAN FRANCISCO — The use of a hemoglobin A1c level of 6.5% or higher to diagnose type 2 diabetes is now mainstream, with formal endorsements from three major U.S. medical associations in 2010 supporting an International Expert Committee's 2009 consensus recommendations.
The World Health Organization and other groups are likely to follow suit, though with greater emphasis on this as an alternative to conventional means of diagnosing diabetes in regions that don't have easy access to standardized assays for HbA1c, Dr. Richard M. Bergenstal said at a meeting sponsored by the American Diabetes Association
He welcomed the change, and the rationale for using HbA1c to diagnose diabetes. “Why do we follow it so closely once you're diagnosed, but pay no attention to it before you're diagnosed?” asked Dr. Bergenstal, president of medicine and science for the ADA and executive director of the International Diabetes Center, Saint Louis Park, Minn.
The International Expert Committee, with members appointed by the ADA, the European Association for the Study of Diabetes, and the International Diabetes Federation, got the ball rolling by publishing a consensus opinion in July 2009 to make HbA1c the preferred test for diagnosing type 2 diabetes (Diabetes Care 2009;32:1327-34).
The ADA translated the international consensus into clinical practice recommendations that were published in its annual update on standards of care in January 2010 (Diabetes Care 2010;33:S11-61). The ADA backed away from calling HbA1c the preferred test, instead saying it's one of four options, but acknowledged that it may become the most popular diagnostic test for type 2 diabetes.
The other, conventional diagnostic criteria are a fasting plasma glucose level of at least 126 mg/dL, an oral glucose tolerance test result of 200 mg/dL or higher, or classic symptoms of hyperglycemia plus a randomly obtained glucose level of at least 200 mg/dL.
The Endocrine Society endorsed the ADA clinical practice recommendations in a separate statement that was issued Jan. 20, 2010. The American Association of Clinical Endocrinologists followed with its own supportive statement on Feb. 1, 2010.
Inevitably, clinicians will have patients whose HbA1c and glucose results conflict, Dr. Bergenstal noted. If one is abnormal and the other is not, repeat the abnormal test, the ADA recommendations say. “If that is still abnormal, you've made the diagnosis,” he said. If, instead, you perform a third test method for confirmation and the result meets diagnostic criteria, diabetes is confirmed, he added.
Results are less clear when a patient has one normal and one abnormal test result, and repeating the abnormal test produces a normal result. “Then you have someone who is obviously on the edge” and who should be retested again in 3-6 months, he said.
Another gray area is the use of HbA1c to define prediabetes (patients at high risk for developing diabetes or cardiovascular disease). The statements from the various groups differ somewhat in how they address this. “I think everyone agrees that for at-risk patients, that's a little bit more of a judgment call,” Dr. Bergenstal said.
The International Expert Committee suggested avoiding the concept of prediabetes because the risk is a continuum with a fairly steady rise in risk as HbA1c levels increase. They identified HbA1c levels of 6.0%–6.4% as “very high risk” while noting that people with lower HbA1c levels also may have increased risk for diabetes if other risk factors are present.
The ADA's 2010 clinical practice recommendations declare HbA1c levels of 5.7%–6.4% to be indicative of high risk, and state that patients with these levels may be referred to as having prediabetes, Dr. Bergenstal said. “At 5.7% we thought the risk was really quite high, and that people deserved to have some kind of program” to prevent diabetes.
The American Association of Clinical Endocrinologists suggested that an HbA1c level of 5.5%–6.4% may be a better cut-off to identify higher-risk patients.
Unlike the glucose tests, HbA1c testing does not require patients to fast before testing and carries several other advantages. Each of the statements supporting HbA1c testing for diabetes diagnosis acknowledged a number of caveats, however, such as recognition that marginally elevated HbA1c values in certain ethnic groups do not necessarily indicate diabetes. HbA1c testing should not be used for diabetes diagnosis in patients with conditions that impair the correlation between HbA1c and average blood glucose, such as iron deficiency or renal disease.
Only standardized, validated laboratory assays for HbA1c were endorsed. Some of the newer point-of-care tests may be sufficiently accurate, but others are not, and more testing is needed before these can be endorsed for diabetes diagnosis, he said.