Race-Based Differences in Retinopathy Risk and HbA1c Levels

According to Yusuke Tsugawa, MD, MPH, from Harvard Medical School in Boston, Massachusetts, and colleagues who published their findings of a cross-sectional study, the results argue against a need for higher HbA_1c cutoffs in blacks.

The authors noted that although an HbA_1c level of 6.5% had been selected as the cutoff for diabetes, it was unclear whether this cutoff was appropriate for all people. "[T]his recommendation did not address the ongoing debate about the interpretation of HbA_1c values among black persons and the possible need for race-based HbA_1c cutoff points," the authors write. "A growing body of evidence from epidemiologic and clinical studies shows that HbA_1c levels are consistently higher among black persons than among white persons, and several studies indicate that the correlation between HbA_1c level and blood glucose level differs between these 2 racial groups."

 

Therefore, to assess the association between retinopathy and HbA_1c, the authors enrolled 3812 non-Hispanic white and black American participants (white, 2804; black, 1008) aged 40 years or older in the current cross-sectional study. After adjustment for age, sex, hypertension, body mass index, and family history of diabetes, logistic regression analysis revealed that compared with the reference category (HbA_1c< 5.5%), the prevalence of retinopathy significantly increased among black participants at an HbA_1c level of from 5.5% to 5.9% (risk difference, 5.3; 95% confidence interval [CI], 1.0 – 9.5; P < .05) compared with an HbA_1c level of from 6.0% to 6.4% for white participants (risk difference, 4.8; 95% CI, 0.5 – 9.1; P < .05).

 

The authors excluded participants with incomplete HbA_1c information, incomplete or ungradable retinal imaging exams, and missing data for other pertinent variables (eg, sex, age, and hypertension). Regarding the baseline characteristics of the participants, black participants were younger, had higher HbA_1c and fasting glucose levels, had a higher body mass index, and were more commonly diagnosed with diabetes.

 

In a further analysis that excluded participants taking oral antidiabetic medication or insulin, the prevalence of retinopathy increased at lower HbA_1c levels for black participants than for white participants (5.5% – 5.9% vs ≥6.5%).

The limitations of the study included the inability to examine the effect of the duration of a specific HbA_1clevel, the lack of a statistically significant interaction between HbA_1c levels and race, and the inability to identify the factors responsible for the differences in HbA_1c levels between white and black participants.

 

Despite the growing call for the use of higher HbA_1c diagnostic cutoffs for blacks, the authors note that their findings do not support this proposal. "The results of our study argue against recommending a higher HbA_1cthreshold for diagnosing diabetes in black persons," the authors write. "Longitudinal studies with larger samples are warranted to determine whether a lower threshold of HbA_1c should be considered for the diagnosis of diabetes in this population."