Glycosylated Hemoglobin Associated With Diabetes Risk

From Medscape Medical News
Emma Hitt, PhD

February 23, 2011 — A glycosylated hemoglobin (HbA1c) level equal to or more than 5.0% is associated with a progressively and significantly increased risk for diabetes, with greatest risk for those with an HbA1c level of 6.0% to 6.4%, according to the findings of an historical cohort study.
Levels of HbA1c were also found to be an independent risk factor for type 2 diabetes, according to the findings of a second study.

Peiyao Cheng, MS, with the Department of Veterans Affairs Medical Center, in Tampa, Florida, and colleagues reported their findings online February 2 in Diabetes Care. A second study by Enzo Bonoro, MD, with the Section of Endocrinology and Metabolism, at the University of Verona, in Verona, Italy, and colleagues was reported online February 9 in Diabetes Care.

The American Diabetes Association indicates that HbA1c level can be used to diagnose diabetes, but its value in the prediction of type 2 diabetes is poorly understood. Two studies investigated HbA1c as a predictor of diabetes. Cheng and colleagues' study was designed to determine the ability of HbA1c to predict the incidence of a diabetic diagnosis. The second study, by Bonoro and colleagues, evaluated how high-to-normal HbA1c levels predict type 2 diabetes.

Cheng and Colleagues

Cheng and colleagues identified more than 12,000 nondiabetic patients with a baseline HbA1c level of 6.5% using electronic medical record data. These patients were tracked for 8 years for a subsequent diagnosis of diabetes.

During an average follow-up of 4.4 years, diabetes developed in 26.9% of patients. When compared with the reference group (HbA1c level < 4.5%), participants with an HbA1c level of 4.5% to 4.9% were at no significant increased risk for incident diabetes.
However, the incidence of diabetes progressively and significantly increased among patients with an HbA1c level above or equal to 5.0%, and a significantly increased risk was evident for those with an HbA1c level of 6.0% to 6.4% (P = .0001).

The respective multivariable-adjusted odds ratios for patients with HbA1c values from 5.0% to 5.4%, 5.5% to 5.9%, and 6.0% to 6.4% were 1.70 (95% CI, 1.21 - 2.36), 4.87 (95% CI, 3.49 - 6.79), and 16.06 (95% CI, 11.40 - 22.65).

"These data show a progressive risk for developing diabetes when HbA1c is ≥5.0%, with nominal risk below that level," Dr. Cheng and colleagues conclude. The researchers developed a risk calculator to estimate the 5-year risk for diabetes based on these and other clinical data.

Bonoro and Colleagues

The second study also found that high-to-normal levels of HbA1c were a risk factor for diabetes. "To the best of our knowledge, this study is the first to examine how baseline HbA1c predicts HbA1c-diagnosed diabetes," Dr. Bonoro and colleagues note.

The researchers measured HbA1c level in 919 Caucasian participants, aged 40 to 79 years. New cases of type 2 diabetes were recorded during a 15-year follow-up period.

"The findings of the current study confirm a progressively increased risk of type 2 diabetes across categories of HbA1c and clearly document that subjects with high-normal HbA1c have a strong risk of developing type 2 diabetes..., "Dr. Bonoro and colleagues conclude.

According to the researchers, their findings support the American Diabetes Association recommendations of using HbA1c level for diabetes risk stratification and targeting participants with high-normal levels with preventive strategies.

Diabetes Care. Published online February 2, 2011. Abstract