Inaccuracy in measuring glycated albumin concentration by thiobarbituric acid colorimetry and by boronate chromatography.

We compared thiobarbituric acid colorimetry and boronate chromatography for measuring glycation of serum proteins. With 14C-glycated human albumin as a test material, both methods were acceptably linear and precise. However, comparable estimates (mmol/L) of albumin glycation ranged from 0.22 for thiobarbituric acid to 0.05 for boronate, representing yields relative to [14C]glycosylprotein of 42% and 10%, respectively. The low yield with thiobarbituric acid was corroborated independently on the basis of kinetic differences between the reactions of fructose standards and of glycosylprotein, leading to underestimation of glycosylprotein concentration. The lower estimate of glycosylprotein by boronate chromatography was related to an apparent requirement for two [14C]glyco groups per albumin molecule to effect binding.