Reproducibility for the Diagnosis of Abnormal Glucose Tolerance Is Excellent for A1C and Glycated Albumin but Only Moderate for Fructosamine

A1C represents glycated hemoglobin A and is a non-fasting measure of average glycemia which has been used since 2010 to diagnose abnormal glucose tolerance (Abnl-GT) (a summary term for diabetes and prediabetes). However, A1C may not correlate with average glucose in the presence of anemia, G6PD deficiency and certain hemoglobinopathies. Two non-fasting markers of glycemia which have been proposed as alternatives to A1C are fructosamine (FA) and glycated albumin (GA). FA is a measure of all plasma glycated proteins. Whereas GA is a subfraction of FA. Emerging data suggests that in the diagnosis of Abnl-GT, GA is superior to FA. Critical to the value of a diagnostic test is assessing reproducibility. Therefore, we examined the reproducibility of A1C, FA and GA by performing all three tests 9±4d (mean±SD) apart in 209 African-born Blacks living in the Washington, DC area. Diagnostic sensitivity of A1C, FA and GA for the detection of Abnl-GT was determined by thresholds at the upper quartile of each, specifically ≥5.7%, 235 umol/L and 14.6%, respectively. A1C was assessed by high performance liquid chromatography, FA by colorimetric nitroblue tetrazolium assay and GA by enzymatic assay. Coefficients of variation (CV) were calculated. Kappa statistic (k-statistic) was used to measure diagnostic reproducibility. Strength of agreement by k-statistic is: slight: 0.0 to 0.20, fair: 0.21-0.40, moderate: 0.41-0.60, substantial: 0.61-0.80; excellent: 0.81-1.0. The CV for A1C, FA and GA were: 2%, 3% and 2% respectively, and the k-statistics were: 0.86, 0.59, 0.89 respectively. In short, the diagnostic agreement between A1C and GA on different days was excellent but only moderate for FA. This may explain why GA appears to be a better measure of Abnl-GT than FA. Variation in FA may be greater than the variation in GA because FA encompasses all plasma proteins rather than specifically albumin. Disclosure J.Gatete: None. B.R.Schenk: None. J.Hurston: None. C.Dubose: None. L.Mabundo: None. C.Worthy: None. R.Jagannathan: None. D.B.Sacks: Other Relationship; Sebia, Trinity. A.E.Sumner: None.