Acanthocytes in the Urine: Useful tool to differentiate diabetic nephropathy from glomerulonephritis?

Quantitation of urinary protein excretion is used extensively for diagnostic and prognostic purposes and to assess the effects of therapy. The method most commonly used to measure urinary protein relies on 24-hour urine collections, which are time consuming, cumbersome, and often inaccurate. We reasoned that the urinary protein/creatinine ratio in a single voided urine sample should correlate well with the quantity of protein in timed urine collections. In a study of 46 specimens we found an excellent correlation between the protein content of a 24-hour urine collection and the protein/creatinine ratio in a single urine sample. The best correlation was found when samples were collected after the first voided morning specimen and before bedtime. We conclude that the determination of the protein/creatinine ratio in single urine samples obtained during normal daylight activity, when properly interpreted by taking into consideration the effect of different rates of creatinine excretion, can replace the 24-hour urine collection in the clinical quantitation of proteinuria. In the presence of stable renal function, a protein/creatinine ratio of more than 3.5 (mg/mg) can be taken to represent "nephrotic-range" proteinuria, and a ratio of less than 0.2 is within normal limits.

A prospective study of the prevalence and causes of persistent albuminuria (greater than 300 mg/24 hr) was conducted in non-insulin-dependent diabetic (NIDDM) patients, age less than 66 years, attending a diabetic clinic during 1987. All eligible patients (N = 370) were asked to collect at least one 24-hour urine sample for albumin analysis. Urine collection was obtained in 224 males and 139 females (98%). Fifty patients (7 women) suffered from persistent albuminuria (13.8%). The prevalence of albuminuria was significantly higher in males (19%) than in females (5%). A kidney biopsy was performed in 35 patients (70%). The kidney biopsies revealed diffuse and/or nodular diabetic glomerulosclerosis in 27 patients (77%), while the remaining eight patients (23%) had a variety of non-diabetic glomerulopathies, such as minimal lesion and mesangioproliferative glomerulonephritis. Diabetic retinopathy was present in 15 of 27 patients (56%) with diabetic glomerulosclerosis, while none of the eight patients with a non-diabetic glomerulopathy had retinopathy. Our cross sectional study has revealed a high prevalence of albuminuria and of non-diabetic glomerulopathy as a cause of this complication in NIDDM patients. Presence of diabetic retinopathy strongly suggests that a diabetic glomerulopathy is the cause of albuminuria. Albuminuric non-insulin-dependent diabetic patients without retinopathy require further evaluation, that is, kidney biopsy.

To determine the risk factors for adverse renal outcome in type 2 diabetic patients who underwent renal biopsy and were followed-up longitudinally. We examined 68 consecutive patients with type 2 diabetes during the period of 1985-1999 who underwent renal biopsy for proteinuria > or =1 g/day, renal involvement (proteinuria or renal impairment) at the absence of retinopathy, renal involvement with duration of diabetes or =700 micromol/l) included proteinuria > or = 2g/day (P = 0.0087), SCr >120 micromol/l (P = 0.0005), presence of retinopathy (P < 0.00001) at the time of biopsy, and biopsy showing DGS (groups I and II) (P = 0.035). On multivariate analysis, retinopathy was the only independent variable correlated with end-stage renal failure. This study also showed that the association of hematuria or proteinuria with the absence of retinopathy constitutes the strongest indication for a nondiabetic lesion (positive predictive values of 94%). Patients with type 2 diabetes undergoing renal biopsy constitute a heterogeneous group by their clinical presentations and underlying pathology, but longitudinal studies on the renal outcome of these patients remain limited. Our study showed that renal biopsy is indicated in selective diabetic patients because of potentially treatable nephropathy and of a better prognosis than DGS.