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Abnormal Glucose Tolerance Is Increasing in Sub-Saharan Africans

According to the International Diabetes Federation, by the year 2035, 41.5 million sub-Saharan Africans will be diagnosed as diabetics and 66 million will be diagnosed as pre-diabetics…

This is a 100% increase in the occurrence of diabetes, and it’s the highest predicted increase in the world. To find out whether abnormal glucose tolerance in Africans is being tested correctly as well as whether hemoglobinopathies such as sickle-cell could be affecting tests, researchers conducted a study using data from The Africans in America Study.

The researchers examined two common tests, hemoglobin A1C and fasting plasma glucose (FPG) separately and in combination. Among Africans, a sickle cell trait occurs in 10-40% of population, and Hemoglobin C trait occurs in 2% of African Americans but is much more common in Africa.

A total of 216 African immigrants performed an oral glucose tolerance test (OGTT). Among the participants, 68% were male with age 37 +/- 10 years, range 20-64 years; BMI 27.6 +/- 4.6 kg/m2, range 18.2-41.2 kg/m2. All participants were self-identified as healthy and denied any history of diabetes or diabetic symptoms. Abnormal glucose tolerance was defined as 2-h glucose greater than or equal to 7.8 mmol/L.

The results demonstrated that the combination of FPG and A1C sensitivities were not different by hemoglobin status (all P > 0.6). The combination of FPG and A1C test sensitivities were higher compared to either test alone (all P values ≤ 0.01).

  • Variant hemoglobin was demonstrated in 21% (46 of 216)
  • Abnormal glucose tolerance occurred in 33% (72 of 216)
  • OGTT (2-h glucose ≥ 7.8 mmol/L)
  • Sensitivities of FPG for total, normal, and variant hemoglobin groups: 32%, 32%, and 33%, respectively
  • Sensitivities for A1C were 53%, 54%, and 47%
  • FPG and A1C combined: sensitivities were 64%, 63%, and 67%

The authors concluded that there was no significant difference in sensitivity of A1C by variant hemoglobin. When determining the diagnosis of abnormal glucose tolerance in Africans, the sensitivity of A1C and FPG combination test was significantly better than either test alone.

Practice Pearls:

  • A combination test of FPG and A1C is superior over either test alone.
  • There was no significant difference in sensitivity of A1C by variant hemoglobin.
  • The limitations of this study included the small number of people, that analyses were based on single determinations of A1C, FPG, and 2-h glucose, and cross-sectional design.

Sumner AE, Thoreson CK, O’Connor, MY, et al. Detection of Abnormal Glucose Tolerance in Africans Is Improved by Combining A1C With Fasting Glucose: The Africans in America Study. Diabetes Care 2015; doi: 10.2337/dc14-1179