Disparities in A1C

Disparities in Hemoglobin A1C May Require New Preventive Strategies

 

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According to a new study published in the Annals of Internal Medicine[1] you may want to reconsider the threshold at which you refer your black patients with diabetes for eye exams. Researchers from Boston’s Beth Israel Deaconess Medical Center used data from the 2005 to 2008 National Health and Nutrition Examination Survey (NHANES) to determine that black patients have a higher risk of diabetic retinopathy at any given hemoglobin A1C level between 5% and 7%. In addition, the higher risk at a hemoglobin A1C level of 5.5% to 5.9% for blacks was “Comparable to the risk at a hemoglobin A1C level of 6.0% to 6.4% for whites, indicating that black people may be more vulnerable to high A1C status than whites,” according to lead author Yusuke Tsagawa.

Diabetes has historically been diagnosed based on blood glucose tests, which can fluctuate from day to day. But in 2010, the International Expert Committee recommended adding hemoglobin A1C as a diagnostic metric because it is a more reliable test that reflects average blood sugar over the past 2 to 3 months.

In line with the Expert Committee’s recommendation, the World Health Organization and the American Diabetes Association subsequently adopted a hemoglobin A1C level of 6.5% or higher as the new diagnostic metric for diabetes. For people who do not have diabetes, a normal hemoglobin A1C level is around 5%.

Many studies have already indicated that hemoglobin A1C levels are consistently higher in blacks than in whites, even though underlying blood sugar levels are similar.[2,3] So the researchers used the NHANES data to determine if a higher A1C cutoff level should be used to diagnose diabetes in blacks than in whites, or if there should be a single cutoff for all races. Given the evidence of naturally higher A1C levels among blacks, researchers expected to find a delayed development of retinopathy in blacks compared to whites. Instead, the data showed that the A1C level at which the risk of retinopathy begins to increase was paradoxically lower in blacks compared to whites. The authors believe that these results don’t support a higher HbA1C threshold for diagnosing diabetes in black people.

It’s not clear why A1C levels are higher in blacks than in whites. According to senior author Christina Wee, MD, MPH, “This may be due to biological differences or socio-behavioral differences including disparities in access to health and preventive care, which often lead to dramatically different policy implications. We’re unclear on the cause, but we’re certain it warrants further investigation.” Other research suggests that the disparity in A1C levels may be due to differences in the turnover of red blood cells, how fast glucose is attached or released from red blood cells, or racial differences in blood sugar levels pre- or postprandially.

The bottom line? At this time, there appears to be no reason to raise the A1C cutoff threshold for blacks. But regardless of their A1C levels, you may want to monitor black patients more closely for early diabetic complications, such as retinopathy or nephropathy, and to refer black patients with diabetes for eye exams earlier in the course of the disease.

 

Jill Shuman, MS, ELS
Published on September 4, 2012

 

References

  1. Tsugawa Y, Mukamal K, Davis R, et al. Should the hemoglobin A1C diagnostic cutoff differ between blacks and whites? A cross-sectional study.  Ann Intern Med. 2012;157:153-159.
  2. Herman WH, Ma Y, Uwaifo G, et al. Differences in A1C by race and ethnicity among patients with impaired glucose tolerance in the diabetes prevention program. Diabetes Care. 2007;30:2453-2457.
  3. Saydah S, Cowie C, Eberhardt MS, et al. Race and ethnic differences in glycemic control among adults with diagnosed diabetes in the United States. Ethn Dis. 2007; 17:529-535.