Estimation of the Glycation Gap in Diabetic Patients With Stable Glycemic Control

OBJECTIVE The glycation gap (the difference between measured A1C and the value predicted by regression on fructosamine) is stable and is associated with microvascular complications of diabetes but has not hitherto been estimated within a clinically useful time frame. We investigated whether two determinations 30 days apart suffice for a reasonably reliable estimate if both A1C and fructosamine exhibit stability. RESEARCH DESIGN AND METHODS We studied 311 patients with type 1 or type 2 diabetes for whom simultaneous measurements of A1C and serum fructosamine had been made on at least two occasions separated by 1 month (t(0) and t(1)). Glycemia was deemed stable if A1C(t(1)) - A1C(t(0)) and fructosamine(t(1)) - fructosamine(t(0)) were both less than their reference change values (RCVs). Instantaneous glycation gaps [gg(t(0)) and gg(t(1))] and their mean (GG), were calculated using the data from all stable patients for the required regression. RESULTS Stable glycemia was shown by 144 patients. In 90% of unstable case subjects, a change in medication was identified as the cause of instability. Among 129 stable patients with an average of eight gg determinations prior to t(0), GG correlated closely with the mean of these prior determinations (r(2) = 0.902, slope 1.025, intercept -0.038). CONCLUSIONS The glycation gap can be calculated reliably from pairs of A1C and fructosamine measurements taken 1 month apart if these measurements satisfy the RCV criteria for glycemic control.