Improved Detection of Abnormal Glucose Tolerance in Africans: The Value of Combining Hemoglobin A1c With Glycated Albumin

Abstract

Objective: In African-born Blacks living in America, we determined by BMI category 1) prevalence of abnormal glucose tolerance (Abnl-GT) and 2) diagnostic value and reproducibility of hemoglobin A_1c (HbA_1c), fructosamine, and glycated albumin (GA).

Research design and methods: Participants (n = 416; male, 66%; BMI 27.7 ± 4.5 kg/m² [mean ± SD]) had an oral glucose tolerance test with HbA_1c, GA, and fructosamine assayed. These glycemic markers were repeated 11 ± 7 days later. Abnl-GT diagnosis required 0 h ≥5.6 mmol/L (≥100 mg/dL) and/or 2 h ≥7.8 mmol/L (≥140 mg/dL). Thresholds for HbA_1c, GA, and fructosamine were the values at the 75th percentile for the population (39 mmol/mol [5.7%], 14.2%, and 234 μmol/L, respectively).

Results: Abnl-GT prevalence in the nonobese was 34% versus 42% in the obese (P = 0.124). Reproducibility was excellent for HbA_1c and GA (both κ ≥ 0.8), but moderate for fructosamine (κ = 0.6). Focusing on HbA_1c and GA in the nonobese, we found as single tests the sensitivities of HbA_1c and GA were 36% versus 37% (P = 0.529). Combining HbA_1c and GA, sensitivity increased to 58% because GA identified 37% of Africans with Abnl-GT not detected by HbA_1c (P value for both tests vs. HbA_1c alone was <0.001). For the obese, sensitivities for HbA_1c, GA, and the combined tests were 60%, 27%, and 67%, respectively. Combined test sensitivity did not differ from HbA_1c alone (P = 0.25) because GA detected only 10% of obese Africans with Abnl-GT not detected by HbA_1c.

Conclusions: Adding GA to HbA_1c improves detection of Abnl-GT in nonobese Africans.

Trial registration: ClinicalTrials.gov NCT00001853.

Figure 1

Successful diagnostic test by BMI category in participants with Abnl-GT. The diagnostic color coding: red for HbA_1c, blue for GA, and purple for both tests.

Figure 2

Sensitivities for the diagnosis of Abnl-GT by BMI category for HbA_1c and GA singly and combined. A: Nonobese: sensitivities for HbA_1c, 36%; GA, 37%; and HbA_1c plus GA, 58%. Corresponding specificities were 80%, 75%, and 60%, respectively. B: Obese: sensitivities for HbA_1c, 60%; GA, 27%; and HbA_1c plus GA, 67%. Corresponding specificities were 80%, 94%, and 74%, respectively. C: Whole cohort: sensitivities for HbA_1c, 43%; GA, 34%; and HbA_1c plus GA, 61%. Corresponding specificities were 80%, 80%, and 63%, respectively. Data are mean (95% CI). ***P < 0.001.

Figure 3

Participant characteristics with Abnl-GT according to diagnostic test: A: BMI, B: WC, C: VAT. In each panel: 1 is HbA_1c or HbA_1c and GA; 2 is GA-alone. Data presented as mean ± SE. *P < 0.05; ***P < 0.001.