Racial difference in A1C may be biologic variation

By Megan Rauscher

NEW YORK (Reuters Health) - Among U.S. adults with impaired glucose tolerance, A1C levels are higher in blacks, Hispanics, American Indians and Asians than in whites, even after considering numerous factors likely to affect glucose levels.

A1C level is the percentage of glucose attached to hemoglobin, a molecule in red blood cells. A1C reflects the average glucose level over the previous 3 to 4 months; levels that exceed 7.0 percent are considered too high.

In an interview with Reuters Health, Dr. William H. Herman, of University of Michigan Health System, Ann Arbor, noted that "a lot of literature consistently shows higher hemoglobin A1C levels among U.S. racial and ethnic minority groups, and it's always been attributed to differences in care or differences in glycemic control. Our data suggest that it might reflect differences in biology and the way hemoglobin is glycated across those groups."

In other words, a particular A1C may not reflect the same level of glycemia in different racial and ethnic groups.

Using data from the Diabetes Prevention Program, Herman and colleagues compared A1C levels by race and ethnicity among 3,819 adults with impaired glucose tolerance before and after accounting for factors that differed among the groups or were likely to affect glycemia.

Some of these factors included age, sex, education, blood pressure, body fat, red blood cell levels, fasting glucose and glucose levels after a meal, and insulin resistance.

According to the team's report in the current issue of Diabetes Care, the average A1C was 5.91 percent. After accounting for other potentially influential factors, the researchers found that A1C levels among whites were 5.78 percent, compared with 5.93 percent, 6.00 percent, 6.12 percent, and 6.18 percent, respectively, among Hispanics, Asians, American Indians, and blacks.

These findings, the researchers write, "raise the possibility that A1C may not be valid for assessing and comparing glycemic control across racial and ethnic groups or as an indicator of health disparities."

"Hemoglobin A1C may be affected by factors other than glycemia and it may not be an accurate measure of average blood glucose levels, particularly across US racial and ethnic minority groups," Herman told Reuters Health.

The findings, the study team writes, also raise the "important question of whether A1C can be used as a diagnostic test for diabetes."

SOURCE: Diabetes Care, October 2007.