March 20, 2015
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Higher HbA1c cut-off improves poor HbA1c-OGTT agreement in patients with obesity

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In patients with overweight and obesity, increasing the HbA1c threshold for prediabetes appears to significantly reduce the discordance between HbA1c and oral glucose tolerance test criteria, according to recent findings.

“In this study, we aimed to evaluate whether obesity affected the performance of HbA1c in diagnosing diabetes and prediabetes against a standard [oral glucose tolerance test], which was partly mediated by oxidative stress, and to identify the optimal HbA1c cut-offs in normal body weight, overweight and obese populations in a large cross-sectional study in Harbin, China,” the researchers wrote.

Changhao Sun, MD, PhD, of Harbin Medical University, and colleagues evaluated 4,325 participants in a population-based cross-sectional study. Individuals identified for inclusion in the study were between the ages of 20 years and 74 years; had not been previously diagnosed with diabetes; were identified through fasting plasma glucose (FPG) and 2-hour plasma glucose criteria; had same-day measurements of FPG, oral glucose tolerance test (OGTT) and HbA1c; had no missing data for BMI or waist circumference; and did not have anemia, liver disease or chronic kidney disease.

The researchers found that concordance between HbA1c criteria and OGTT decreased as BMI increased. The structural equation modeling analysis revealed a significant association between BMI and HbA1c in normal glucose tolerance and participants with prediabetes, but not in those with diabetes.

At 80% specificity, the optimal cut-off values for prediabetes were 5.6% for normal weight, 5.7% for overweight and 6% for obesity. At a specificity of 97.5%, the cut-off values for diabetes were 6.4% for normal weight, 6.5% for overweight and 6.5% for obesity. After applying the new HbA1c cut-off points, the agreement in participants with obesity was almost equal to that of participants with normal weight.

“In summary, when the [American Diabetes Association] HbA1c criteria are used for glycemia classification, HbA1c between 5.7% and 6.4% should be interpreted considering BMI, but not in case of HbA1c 6.5% [or more],” the researchers wrote. “Under the background of the incidence of obesity quickly increasing all over the world, a fixed HbA1c cut-off value is not suitable for screening prediabetes in the population with large BMI variation. This study raises the possibility that personalized cut-off values considering BMI and other confounding factors for glycemia classificiation may be more appropriate.” – by Jennifer Byrne

Disclosure: The researchers report no relevant financial disclosures.