A colorimetric method for the estimation of serum glycated proteins based on differential reduction of free and bound glucose by sodium borohydride

A new colorimetric method based on the phenol-sulfuric acid reaction is described for the estimation of serum glycated proteins by the differential reduction of free glucose and hexose bound nonenzymatically with 2.0 and 20 mg of NaBH₄ in 0.02 ml of serum, respectively, at room temperature for 15 min. The values (μg hexose/mg protein) in control subjects (n = 60) and diabetics (n = 90) were estimated to be 5.60 ± 0.85 and 10.8 ± 1.6, respectively. The increase was highly significant (P < 0.001) in diabetics. The serum glycated protein levels correlate well with fasting blood sugar values (r = 0.77, P < 0.001, n = 25). There was also a highly significant correlation between glycated protein level and glycated albumin value in individual serum samples (r = 0.85, P < 0.001, n = 25). Values of borohydride reducible glyco-groups bound to serum proteins also correlated well with serum glycated protein levels (r = 0.96, p < 0.001, n = 20) determined by the thiobarbituric acid assay method. The method is found to be simple and rapid, with a coefficient of variations of ±3.8%.