Compared with the gold standard screening test for Type 2 diabetes, the hemoglobin A1c blood test has a risk of underdiagnosing diabetes in elderly Asians using the recommended cutoff of 6.5 percent or greater to indicate diabetes, authors of a new study find. They will present the results Sunday at The Endocrine Society’s 92nd Annual Meeting in San Diego.
“The hemoglobin A1c is a useful and convenient screening test for diabetes. However, we may need age-specific reference ranges, rather than using a single cutoff level across the board,” said lead author Tunn Lin Tay, MD, an endocrinology fellow at Singapore’s Changi General Hospital.
Last year the American Diabetes Association endorsed a hemoglobin A1c result of 6.5 percent or greater as a means of diagnosing Type 2 diabetes. A1c has long been a monitoring test of diabetic patients’ long-term blood glucose (sugar) control. Traditionally, doctors screen for diabetes using one of two blood tests: the fasting plasma glucose test or oral glucose tolerance test. The latter, which experts consider the best test to identify diabetes and prediabetes, tests blood sugar before and after the patient drinks a sugary solution.
Advantages of the A1c test for screening are that it does not require patients to fast for eight hours and is simpler to perform than a two-hour oral glucose tolerance test.
However, some diabetes experts say the A1c test may be misleading in certain ethnic groups, such as blacks. Tay says no data are available on the test’s accuracy in a Southeast Asian population despite their high prevalence of diabetes worldwide. Now her study results in a predominantly Chinese population suggest that the A1c test using the current cutoff may be less reliable for people above the age of 72.
Using the A1c and the oral glucose tolerance test, Tay and her colleagues screened 90 patients with no prior diagnosis of Type 2 diabetes. They divided patients, who ranged in age from 20 to 93 years, into four subgroups by age: 50 and younger, 50.1 to 59, 59.1 to 72, and older than 72.
The oral glucose tolerance test found that 40 of the 90 patients had Type 2 diabetes. In the whole study population and in patients younger than 72, the best A1c cutoff for diagnostic accuracy was 6.2 percent, the authors reported. Under existing A1c criteria, 6.2 percent means the person does not yet have diabetes.
In this Asian population, the A1c test declined in accuracy as age increased, according to Tay. Among people older than 72, the test had a low diagnostic sensitivity (54.5 percent), and thus a high chance of missing the diagnosis of diabetes in those with the disease.
“A hemoglobin A1c cutoff at 6.2 percent had a 45.5 percent chance of missing patients with diabetes in the oldest group,” she said. “We found that 6 percent is the best cutoff point in patients older than 72 years.”
Based on their results, Tay said, “If clinicians screen elderly patients, especially Asians, using the hemoglobin A1c test, they should confirm the diagnosis using the oral glucose tolerance test.”
A research grant from the Endocrine and Metabolic Society of Singapore helped fund this study.
