The usefulness of micro- and macrochromatographic determinations of glycohemoglobin in diabetic patients with nephropathy.

Determination of glycohemoglobin in blood (HbA1) represents an established measure of glycemic control in diabetic patients. In patients with uremia, however, the determination can be subject to pitfalls which may limit its reliability. In order to evaluate the clinical usefulness of HbA1 determinations in diabetic patients with nephropathy, concentrations of HbA1 and its subfractions HbA1c and HbA1a+b were measured by micro- and macrocolumn chromatography in 58 diabetic and 80 non-diabetic patients with impaired renal function. Fifteen diabetic patients without nephropathy and 15 healthy subjects served as controls. The concentrations of HbA1 and its subfractions were significantly higher in non-diabetic patients with nephropathy than in healthy controls. A positive correlation was seen between HbA1 and plasma glucose concentrations in all subjects, and between HbA1 and serum urea and creatinine concentrations in the non-diabetic subjects. When measured repeatedly in the same patient there was a positive correlation between HbA1 and plasma glucose concentrations in diabetic patients with azotemia. There was no change in HbA1 concentrations measured immediately before and after hemo- or peritoneal dialysis. The increase of chromatographically determined HbA1 concentrations in azotemic patients is most likely due to the joint action of carbamylation of hemoglobin with urea derived cyanate and deterioration of glycemic control induced by azotemia. Despite these problems, chromatographically determined HbA1 is still a clinically useful measure of glycemic control in diabetic patients with nephropathy. This presumes repeated measurements in the same patient and the use of appropriate reference levels which consider the degree of renal impairment.