In 47 patients with diabetic nephropathy (29 type I, 18 type II) renal function and blood pressure (BP) (treated with or without an angiotensin-converting enzyme [ACE] inhibitor, enalapril [10 mg], in 38 hypertensive patients) were followed over 4 years. A percutaneous renal biopsy was performed in all patients initially and repeated in a representative 19 patients with treated hypertension after 4 years. Mean glomerular volume (MGV), interstitial fibrosis (IF), capillary volume, and sclerosed glomeruli (GS) were measured histomorphometrically. Mean fall in creatinine clearance (CCr) was 11.8% after 4 years with no difference between treatment groups or type of diabetes. BP both initially and during treatment correlated with initial and final serum creatinine and CCr (P < 0.01). There were no histomorphometric differences between type I and type II patients or hypertension treatment groups. Initial IF correlated with initial and final serum creatinine and CCr (P < 0.05) in all patients and type I patients alone, MGV correlated inversely with CCr in type I patients (P < 0.05). After 4 years, IF (24.8 vs. 30.0%, P < 0.01) and GS (26 vs. 37%, P < 0.05) increased significantly, and increase in IF correlated with fall in CCr (P < 0.01). Proteinuria and HbA1 did not correlate with indexes of function or structure. In this longitudinal study of patients with diabetic nephropathy, there was a close relation between BP and renal function but no difference between treatment with enalapril and other hypertensive agents. The correlations between renal function and histology at entry and after 4 years suggest that IF is a co-determinant of renal function in diabetic nephropathy.

Coexistent renal pathology with diabetic glomerulosclerosis was found in 38 of 136 (28%) consecutive renal biopsies performed primarily for proteinuria in individuals with diabetes mellitus. The histological lesions found were glomerulonephritis (14), focal tubulointerstitial disease (23), and amyloidosis (1). Significant microscopic haematuria was present in 66% of all patients and did not help to distinguish non-diabetic disease. The severity of diffuse diabetic glomerular disease was independently associated with duration of diabetes, raised plasma creatinine, the presence of hypertension, clinical retinopathy and neuropathy, but not with type of diabetes, degree of proteinuria or glycosylated haemoglobin at the time of biopsy. Diffuse interstitial fibrosis was related to the severity of glomerular disease and, if severe, also with a significantly (p less than 0.01) higher plasma creatinine. Coexisting renal disease was found to be associated with a significantly higher plasma creatinine (p less than 0.01) independent of the severity of diabetic glomerulopathy. Coexistent pathology is a not uncommon finding in renal biopsies from diabetic patients with proteinuria. These lesions and their underlying causes may not only influence the renal function and natural history of renal disease in diabetic individuals, but may also determine the response of proteinuria to therapy.

Thirty years following the development of the first radioimmunoassay for albumin, microalbuminuria is widely acknowledged as an important predictor of overt nephropathy in patients with Type 1 diabetes and of cardiovascular mortality in Type 2 diabetes. In addition, there is accumulating evidence to suggest that diabetic patients with microalbuminuria may have more advanced retinopathy, higher blood pressure, and worse dyslipidaemia than patients with normal albumin excretion rates. Recent studies have focused on the role of intervention, principally with antihypertensive therapy and intensive glycaemic control, in reducing microalbuminuria. While successful in reducing urinary albumin excretion it remains to be established whether such therapies will be translated into a reduction in renal failure and decreased cardiovascular morbidity and mortality.

This statement summarises current understanding of the role of microalbuminuria in diabetic nephropathy and describes its natural history and clinical relevance. It outlines core facts and makes recommendations for the management of patients with persistent microalbuminuria.

No abstract