Fructosamine is Not a Reliable Test for the Detection of Hyperglycemia: Insight from the Africans in America Study

Objective: To improve detection of abnormal glucose tolerance (Abnl-GT), attention has moved beyond the oral glucose tolerance test (OGTT), to non-fasting markers of glycemia, specifically, HbA1c, fructosamine (FA) and glycated albumin (GA). Emerging data suggest that in African descent populations, the combination of HbA1c and GA is superior to the combination of HbA1c and FA. However, the diagnosis of Abnl-GT is usually based on tests which are performed only once. As reproducibility of Abnl-GT diagnosis by HbA1c, fructosamine (FA) and glycated albumin (GA) is unknown, reproducibility of Abnl-GT diagnosis by HbA1c, FA and GA were assessed in 209 African-born Blacks living in America. Methods: At Visits 1 and 2 (9 +/- 4 days apart), samples were obtained for HbA1c, FA and GA levels. Glucose tolerance status was determined at Visit 1 by OGTT. Reproducibility was based on the.-statistic and paired t-tests. Thresholds for the diagnosis of AbnlGT by FA and GA which corresponded to an HbA1c of 5.7% were 235umol/L and 14.6%, respectively. Results: Abnl-GT occurred in 38% (80/209). Diagnostic reproducibility was excellent for HbA1c (K >= 0.86) and GA (K >= 0.89), but only moderate for FA (K=0.59). Neither HbA1c nor GA levels varied between visits (both P >= 0.3). In contrast, FA was significantly lower at Visit 2 than Visit 1(P<0.01). Conclusion: As HbA1c and GA provided similar diagnostic results on different days and FA did not, HbA1C and GA are superior to FA in both clinical care settings and epidemiologic studies. Plain Language Summary: Beyond the monitoring of blood glucose levels, HbA1c is now used to diagnose hyperglycemia, but fructosamine and glycated albumin are being evaluated as alternatives when red blood cell factors cause inaccurate HbA1c results. Studies suggest glycated albumin may be a better diagnostic test than fructosamine, but these investigations were poorly designed as conclusions were based on studies done once on a single day. Therefore, in our study, each participant was studied twice with samples drawn one to two weeks apart. We found that the reproducibility of the diagnosis of hyperglycemia made by glycated albumin was excellent but only moderate for fructosamine. This could explain why glycated albumin may be superior to fructosamine in both the care of patients and the design of large population studies.