Black and White Differences in Hemoglobin A1c Levels
Black and White Differences in Hemoglobin A1c Levels
Abstract & Commentary
By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.
Synopsis: American non-Hispanic black persons had higher HbA1c levels than white persons at all levels of glycemia, and this difference increased as glucose intolerance worsened.
Source: Ziemer DC, et al. Glucose-independent, black-white differences in hemoglobin A1c levels: A cross-sectional analysis of 2 studies. Ann Intern Med 2010;152:770-777.
Hba1c values from two previously conducted studies, which included more than 3500 participants that had normal glycemia, prediabetes, or diabetes, were analyzed to adjust for plasma glucose levels and other characteristics. The Screening for Impaired Glucose Tolerance used 1580 volunteers, aged 18-87 years without known diabetes, and measured random glucose and HbA1c as well as a fasting and 2-hour glucose tolerance test. The other data came from the CDC's recurring NHANES III (Third National Health and Nutrition Examination Survey), from which data on 1967 participants with HbA1c levels were obtained; participants older than 40 years had fasting and glucose tolerance testing. Persons receiving treatment for diabetes were excluded from analysis.
Results showed HbA1c levels consistently higher in black vs white populations, ranging from a 0.13 percentage point increase associated with normal glucose tolerance tests, up to a 0.47 percentage point increase in those with diabetes. Diabetes was defined as fasting glucose higher than 125 mg/dL or 2-hour glucose > 199 mg/dL. These differences persisted even after adjusting for other factors such as age, sex, BMI, blood levels of vitamins A, C and E, marital status, and income.
Commentary
As we increasingly utilize HbA1c levels as a measure of glucose control, and even for the initial diagnosis of diabetes, it behooves us to consider that baseline levels may not be identical in all persons. Other factors may decrease HbA1c, such as alcoholism and salicylate use, increase HbA1c with iron-deficiency anemia, or falsely increase HbA1c with chronic dialysis, uremia, and hyperbilirubinemia. However, none of these were thought to be present in any large amount in this study where measurements came from random samples of working people.
It does appear from this study and others1 that black persons have higher HbA1c levels at baseline, no matter what level of glycemia they are associated with, ranging from 0.13 to 0.26 in euglycemia to 0.47 when diabetes is present. Although the reasons for this remain to be explained, the differences may need to be taken into consideration when establishing targets for optimal control; however, what this means for complications and outcomes is unclear. Since research on the benefits of tight control did not factor in these racial differences, there remain lots of unanswered questions about whether black persons should have different HbA1c targets, or would benefit from the tighter control targets that have been shown to be of benefit in population-wide studies.
Reference
1. Herman WH, 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.
American non-Hispanic black persons had higher HbA1c levels than white persons at all levels of glycemia, and this difference increased as glucose intolerance worsened.Subscribe Now for Access
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