Efforts to adopt a more accurate test for diagnosing diabetes may have hit a snag. Comparing the age-old oral glucose tolerance test to the newer hemoglobin A1c test confirms earlier evidence that race may influence test results, Danish researchers report.

“The prevalence of diabetes differed considerably according to diagnostic method,” they write in the Journal of Clinical Endocrinology and Metabolism.

Clinicians have sought a better diabetes diagnostic tool than the oral glucose tolerance test, which measures the body’s response to a large dose of glucose after fasting. Among that method’s weaknesses is the need to average several test results over time for a valid diagnosis. Each glucose tolerance test is only a snapshot in time of how well the body is processing glucose into energy.

The hemoglobin A1c measures how much glucose is attached to the hemoglobin proteins in red blood cells, reflecting blood sugar levels over the 2- to 3-month lifespan of a red blood cell.

Marit Eika Jorgensen and colleagues, at the Steno Diabetes Center and the National Institute of Public Health in Copenhagen, wanted to see if ethnicity influenced results of the two blood tests. They compared results from both in three groups of people: 1,173 Inuits from Greenland, 256 Inuit migrants living in Denmark, and 6,784 Danes.

The researchers also measured baseline fasting blood glucose levels and found that at all levels of blood glucose the “Inuit had significantly higher levels of HbA1c than the Danish participants,” leading to more diagnoses of diabetes in the Inuit population.

Among Greenland Inuits, the prevalence of diabetes, as determined by the hemoglobin A1c test (31.7 percent) was nearly three times higher than when diagnosed using the oral glucose tolerance test (11.2 percent). Comparing the two tests saw a more than doubling of diabetes for Inuits living in Denmark: 21.3 percent using the A1c test vs. 9.8 percent with the glucose tolerance test.

For Danes the jump was not as pronounced: 6.7 percent vs. 4.2 percent.

Previous studies in American populations have shown similar ethnic disparities. Even when glucose tolerance test results were the same, American blacks, Hispanics and Asians had higher hemoglobin A1c levels than whites.

Unmanaged diabetes is associated with many dangers, including heart disease and stroke. The Jorgensen team found, however, that individuals diagnosed with diabetes by the old glucose tolerance test had “a less favorable cardiovascular risk profile” than subjects with diabetic levels of hemoglobin A1c, leading them to conclude that “the new definition of diabetes identifies individuals at lower cardiovascular risk.”

The new test has the potential of defining more people, especially ethnic minorities, as diabetic, which “will have substantial consequences for the healthcare system in terms of diabetes treatment and management,” the authors note.

Dr. Anthony J. Bleyer of Wake Forest University in Winston-Salem, North Carolina, who was not involved in this study, said doctors are moving in large numbers to adopt the hemoglobin A1c test and it “remains an excellent test.”

“The effects of race on a patient’s results won’t make much difference in that patient’s care,” he told Reuters Health, “but it could make a big difference when that patient goes to buy life insurance if a certain cutoff is used to diagnose diabetes.”

“African Americans are more likely to be diagnosed with diabetes if this (difference) is not taken into account,” he said.

“Each doctor and patient wants the test to be accurate, correct? Why should we tolerate it to be just a little bit inaccurate in African Americans,” he asked.

In order to diagnose diabetes, the American Diabetes Association recommends the hemoglobin A1c test, along with other diagnostic tools, without reference to racial differences.

The research that suggests differences in hemoglobin A1c levels in different racial groups is under review. “As with any new studies, the Professional Practice Committee will consider it as they revise the annual Standards of Care,” Dr. Sue Kirkman, the association’s Senior VP of Medical Affairs and Community Information, told Reuters Health in an email. “It’s not clear-cut that there’s a significant clinical difference.”

Dr Gojka Roglic, of the World Health Organization in Geneva, Switzerland, told Reuters Health that a decision has not been made about hemoglobin A1c use “and we are currently reviewing this topic, but not in the context of replacing glucose measurement, but looking at whether HbA1c can be included as an additional test for diabetes.” The issue of ethnic differences “is certainly of interest,” he added.

SOURCE:  Journal of Clinical Endocrinology and Metabolism, online August 25, 2010.