Diagnosing Diabetes: A Danish Study on HbA1c Levels and Ethnicity

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Until this year, the glycated hemoglobin or hemoglobin A1c (HbA1c) test was used only for monitoring patients once they had been diagnosed with diabetes. In January 2010, however, the  American Diabetes Association Standards of Medical Care in Diabetes added the measure of HbA1c  6.5% as a criterion for the diagnosis of diabetes, in addition to the fasting glucose test and the oral glucose tolerance test.  Whether HbA1c should be used as a diagnostic tool has been questioned by some, and studies have shown that African Americans have a higher level of HbA1c for a given level of blood sugar than do non-Hispanic whites. A new study, conducted by Marit Eika Jorgensen and colleagues, at the Steno Diabetes Center and the National Institute of Public Health in Copenhagen, and, published in the Journal of Clinical Endocrinology and Metabolism aimed to  assesswhether ethnicity modified the association between glucose levelsand HbA1c and to compare diabetes prevalence according to diagnosticmethod among Greenland Inuit, Inuit migrants in Denmark, anda general Danish population.

In the study, data from two population-basedsurveys conducted from 1999–2002 were compared with atotal of 7957 individuals, 1173 Inuit participants from theGreenland Population Study, including 256 Inuit migrants inDenmark, and 6784 Danish participants in the Inter99 study.The participants received a standard 75-gram oral glucose tolerance test (OGTT). HbA1c was analyzedby an ion-exchange HPLC Bio-Rad variant (Hercules, California).All analyses were performed in the laboratory at Steno DiabetesCentre.

The results of the study showed the Inuit had significantly higher levels ofHbA1c than the Danish participants at any given level of fastingand 2-hour glucose test and for each category of glucose tolerance:normal glucose tolerance, impaired fasting glycemia, and impairedglucose tolerance. The prevalence of diabetes diagnosed by OGTTwas 11.2% among Inuit residents in Greenland, 9.8% among Inuitmigrants, and 4.2% among Danes vs. 31.7% among Inuit residentsin Greenland, 21.3% among Inuit migrants, and 6.7% among Danesdiagnosed by HbA1c. OGTT-defined diabetes was associated withincreased cardiovascular risk factors compared to HbA1c-defineddiabetes.

The study concluded that the association between glucose and HbA1cis not the same in the two populations. The mechanism behindthis difference is unknown, and studies on long-term consequencesassociated with HbA1c are needed.

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