COMMENTARY

Why Do Black Americans Have Higher A1c Levels Than Whites?

Racial Differences Intrigue Researchers, Inform Diabetes Care

Richard M. Bergenstal, MD; Mark Harmel, MPH

Disclosures

August 17, 2016

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I am part of a team that is trying to answer what I believe is an important clinical question: Do blacks Americans have higher A1c levels than white Americans, and if they do, why? This has been a controversy for the past decade or so.

I have been fortunate to be part of the T1D Exchange, a network that encourages clinical investigators to pose clinical questions. This network of 80 clinics and a coordinating center will then help answer those questions.

We asked: Why do blacks have higher A1c levels than whites? (Many studies have found A1c levels to be 0.8% to 1% higher in blacks than whites.) Is it related to higher blood glucose levels, less access to care, less use of technology, or other social determinants of health? Do blacks have higher blood sugars than whites, and therefore their A1cs are higher? Or do they have blood sugar levels that are similar to those of whites but, at a given glucose level, they glycate or attach glucose onto their red cells much more aggressively?

No one has adequately addressed these questions. There have been a lot of opinions, but no answers.

Solving the Riddle

Because the A1c reflects the most recent 2-3 months of blood sugar levels, we decided that the best way to answer the question was first to use continuous glucose monitoring for 90 days, to measure the blood sugar every day, 24 hours a day, for 3 months. Then we compared the average glucose in whites with their A1c levels and the average glucose in blacks with their A1c levels. That would tell us whether there is a racial difference.

In all, 10 centers participated. We enrolled 208 patients, 104 blacks and 104 whites, ages 8-75 years.

What did we find? We confirmed that blacks have higher A1c levels than whites; in our study, the A1c was about 0.8% higher in blacks. Other studies have found larger (1% to 1.5%) differences.

We should be paying much more attention to blood sugars than to A1c levels to individualize care.

Then, for the first time, we showed that in blacks, glucose attaches onto red cells more aggressively, or at a higher rate than in whites. For a given blood sugar, the A1c was about 0.3% percent higher in blacks than in whites. Thus, with the same glucose level, a black woman would have an A1c level of 8%, but a white woman would have an A1c level of 7.7%—0.3% lower.

In lower A1c ranges around 6.5%, the difference between blacks and whites was about 0.2%, and at higher ranges, with A1c levels of 10%, such as we see in type 1 diabetes, the difference between blacks and whites was about 0.4%-0.5%.

We concluded that the glycation rate in blacks is higher than in whites. The difference is real but relatively small.

Raising New Questions

Next, we asked whether excess glycation was also seen with other proteins in the blood such as albumin and fructosamine. Would those levels be higher in blacks than in whites?

The answer was no, blacks did not glycate those other proteins at a higher rate than whites. Thus, if researchers want to sort out this excess glycation in blacks, they should study the red cell; they should study hemoglobin, not other proteins in the blood.

Finally, after showing that blacks have higher A1c levels than whites, with a small but real excess glycation, we looked across the whole A1c assay and average glucose levels. We confirmed that there was a higher difference in average glucose level and the A1c even within a race.

Within our black cohort and within our white cohort, there was as much as an 80 mg/dL difference in average glucose for the same A1c level. This difference was much greater than the difference between races.

That leads us to the implication that, as a group of people taking care of patients with diabetes, we should be paying much more attention to blood sugars than to A1c levels to individualize care. The A1c is a great marker for risk for complications, but knowing the blood sugar is what we need when we are making management decisions.

In the end, this was a great effort. It was a relatively small question, but an important one. Black Americans have higher A1c levels than white Americans. About one-third to one-half of that difference is related to excess glycation; the rest is caused by too much glucose in the blood, in part because we have not given adequate attention to their care.

We need to sort this out and continue looking at blood sugar levels to personalize care.

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