Detection of abnormal glucose tolerance in Africans is improved by combining A1C with fasting glucose: the Africans in America Study.
Level 3 - non-randomized controlled study
Cross-sectional diagnostic accuracy study comparing index tests against a reference standard (OGTT)
PubMed 25338926 · doi:10.2337/dc14-1179
What was done
An oral glucose tolerance test (OGTT) was conducted in 216 African immigrants in the United States (68% male, mean age 37 ± 10 years, range 20-64 years) to evaluate diagnostic sensitivity against a reference standard (abnormal glucose tolerance defined as 2-h glucose ≥ 7.8 mmol/L). Sensitivities were evaluated for: 1) fasting plasma glucose (FPG) ≥ 5.6 mmol/L, 2) A1C ≥ 5.7% (39 mmol/mol), and 3) FPG combined with A1C, stratified by the presence of heterozygous variant hemoglobins.
What was found
Variant hemoglobin was present in 21% (46/216) of participants, and abnormal glucose tolerance was found in 33% (72/216). Sensitivities of FPG for total, normal, and variant hemoglobin groups were 32%, 32%, and 33%, respectively. Sensitivities for A1C were 53%, 54%, and 47%. Sensitivities for combined FPG and A1C were 64%, 63%, and 67%. Sensitivities did not vary significantly by hemoglobin status (all P > 0.6). Across the cohort, sensitivity was higher for A1C than FPG and higher for the combined tests than for either test alone (all P ≤ 0.01).
Why it matters
Combining A1C with fasting plasma glucose significantly improves sensitivity for detecting abnormal glucose tolerance in African individuals compared with either test alone. Furthermore, the diagnostic sensitivity of A1C does not appear to be compromised by heterozygous hemoglobin variants.
Limits
The cohort was modest in size (n = 216) and limited to African immigrants living in the United States. Specificity, positive predictive values, and negative predictive values were not reported in the abstract.
Cited by
- supports American Diabetes Association publications acknowledge that hemoglobin A1C and fasting glucose miss over half of prediabetes and diabetes cases.