FROM JAMA
African Americans who have sickle cell trait show lower hemoglobin A1c levels at any given concentration of fasting glucose than do those who don’t have sickle cell trait, according to a report published online Feb. 7 in JAMA.
This suggests that HbA1c levels systematically underestimate glucose levels in black patients who carry the trait, who comprise approximately 10% of the African American population, said Mary E. Lacy, a doctoral candidate in the department of epidemiology, Brown University School of Public Health, Providence, R.I., and her associates.
The investigators examined a possible link between HbA1c and sickle cell trait, which affects hemoglobin even though it doesn’t confer sickle cell disease, by analyzing data from two cohort studies involving African American adults. They focused on 4,620 participants who underwent serial HbA1c and plasma glucose measurements during 5-25 years of follow-up. A total of 367 of them had sickle cell trait.
Analysis of 9,062 concurrent assessments of fasting glucose and HbA1c plus 2,001 concurrent assessments of 2-hour postprandial glucose and HbA1c showed mean HbA1c was consistently significantly lower in people with sickle cell trait (mean level, 5.7%) than in those without the trait (mean level, 6%) despite similar glucose values.
“Our results suggest that currently accepted clinical measures of HbA1c do not reflect recent past glycemia in the same way in African Americans with and without sickle cell trait,” Ms. Lacy and her associates said (JAMA 2017 Feb 7. doi: 10.1001/jama.2016.21035).
When used as a screen for prediabetes or diabetes, HbA1c values “systematically underestimate long-term glucose levels,” which means a significant proportion of African American patients will miss the opportunity for treatment. In this study, “using standard clinical HbA1c criteria to identify prediabetes and diabetes resulted in identifying 40% fewer cases of prediabetes and 48% fewer cases of diabetes among participants with sickle cell trait, compared to those without sickle cell trait,” the investigators noted.
“Because black people typically have a higher prevalence of diabetes and experience a number of diabetic complications at higher rates than [those of] white people, the cost of inaccurately assessing risk and treatment response is high,” they added.
The National Heart, Lung, and Blood Institute, the National Institute on Aging, the National Institute on Minority Health Disparities, the Providence VA Medical Center, and the National Institute of Diabetes and Digestive and Kidney Diseases supported the study. Ms. Lacy and her associates reported having no relevant financial disclosures.
