Renal handling of glycated albumin in non-insulin-dependent diabetes mellitus with nephropathy.

Renal handling of glycated albumin in diabetic nephropathy was examined by studies on renal selectivity for glycated albumin in 23 normal controls and 52 patients with non-insulin-dependent diabetes mellitus (NIDDM) with various degrees of nephropathy. The serum and urinary levels of glycated albumin were measured by enzyme-immunoassay with monoclonal antibody to glucitol-lysine residues in human glycated albumin. The diabetic patients were divided into 3 groups according to the albumin index (AI): patients with normoalbuminuria [AI less than or equal to 30 mg/g creatinine(Cr)], with microalbuminuria (30 less than AI less than or equal to 270 mg/g Cr), and with macroalbuminuria (AI greater than 270 mg/g Cr). The renal selectivity for glycated albumin was calculated from the ratio of the urinary to serum level of glycated albumin. In the controls, the renal selectivity was as high as 4.40 +/- 0.48, and significantly higher than those in patients with normo- (2.87 +/- 0.29), micro- (1.72 +/- 0.20) and macroalbuminuria (1.26 +/- 0.23). The renal selectivity was inversely correlated with the AI in diabetic patients (r = -0.58, P less than 0.01). These data indicate that glycated albumin was selectively excreted in the urine and that the renal selectivity in diabetic patients gradually decreased to a value of 1 with increase in albuminuria. When the patients with normoalbuminuria were divided into two subgroups with high and low albumin excretion, the renal selectivities for glycated albumin in both subgroups were still significantly lower than that in controls. These results suggested that early diabetic nephropathy which cannot be detected clinically by albuminuria can be diagnosed by measurement of renal selectivity for glycated albumin.