Abstract
In the measurement of glycosylated protein (G-P), the presence of free glucose in the plasma or serum results in falsely high values. To avoid such interference of free glucose, sample dialysis before assay has been used. The dialysis, however, requires many hours and the possibility of partial release of protein-bound glucose during the dialysis has been suggested.
In the present study, plasma G-P was measured by an improved method, treating the plasma with trichloroacetic acid (TCA) before assay.
The G-P values of normal plasma samples, with various amounts of previously added glucose, showed a linear increase in absorbance. However, pretreatment of these plasmas with TCA completely abolished the interference of glucose. The lowest G-P values were obtained in dialyzed samples, while nontreated samples showed the highest values. The difference among the nontreated, TCA treated and dialyzed samples was found to be highly significant (p<0.001). Further studies on the effects of TCA on the hydrolysis were carried out. Dialyzed plasmas were divided into three groups according to their pretreatment before assay (i.e. no treatment, TCA treatment or addition of a small dose of TCA after TCA treatment). The levels of G-P were proportional to the dose of TCA. This result suggests that the TCA enhanced the hydrolysis since TCA did not affect the thiobarbituric acid (TBA) reaction.
The G-P values of normal subjects and diabetic patients were 1.32±0.13 and 2.0±0.66n mol HMF/mg of protein (mean±SD), respectively. When the diabetic group was classified into four groups according to the mean levels of plasma glucose obtained during the previous 1 week, three groups, i. e. except for that with a mean glucose level of below 100mg/dl, revealed significantly high G-P values as compared to those of normal subjects. The difference among the three groups with a mean glucose level of below 150mg/dl, however, was not significant. The correlation coefficients between the G-P values and plasma glucose levels on the same day or HbAi values were 0.64 and 0.57, respectively.
