Diabetic nephropathy. A clinical study of risk factors in type-I diabetes mellitus

The aim of the study was to evaluate risk factors for the development and progression of diabetic nephropathy. For this purpose, a reliable method of monitoring renal function is necessary. Five different methods of estimating renal function (plasma and renal clearance of 51Cr EDTA, serum creatinine, plasma beta-2-microglobulin and endogenous creatinine clearance) were compared. The risk factors studied were hyperglycaemia, smoking, diabetic cystopathy and dietary protein. All patients were treated for hypertension. The metabolic control was evaluated by assay of HbA1c and repeated estimation of blood glucose. A careful interview about previous and current smoking habits was used for evaluation of the role of smoking. Presence of residual urine, registered with an isotope technique using 131I-Hippuran, was used as the criterion of diabetic cystopathy. Dietary protein intake was studied with a dietary history interview and by measuring the urinary excretion of nitrogen. All five renal function tested evaluated have disadvantages. The most reliable information is given by the combined measurement of plasma clearance and renal clearance of 51Cr EDTA. Hypertension is the most important factor for progression but metabolic control also has an impact, which can be shown when hypertension is adequately controlled. Diabetic patients with nephropathy have smoked more and still smoke more than patients without nephropathy. Diabetic cystopathy is common but with instructions it can be kept constant for several years. Although a correlation of cystopathy to progression is likely, it could not be demonstrated. The study of protein intake does not support the theory of a harmful effect of dietary protein on the development or progression of diabetic nephropathy. By intervening against risk factors, it is possible to achieve a very low progression rate or even to arrest the progression for several years.