The management of glomerulopathy due to diabetes mellitus is a common and important task that all general internists must face. In the United States, diabetes is the leading cause of end-stage renal disease (ESRD). It occurs in 33% of all diabetics. Diabetic nephropathy is a spectrum of progressive renal disease ranging from microalbuminuria (30-300 mg/24 h) to overt nephrotic syndrome and ESRD. In terms of incidence, 30 to 40% of type I diabetics and 15 to 20% of type II diabetics will acquire ESRD in 20 years.
So how does one screen for diabetic nephropathy and try to prevent its progression? Urine dipsticks that are commonly found at internists' offices are not sensitive enough to detect microalbuminuria and will only be positive once the albumin level is above 300 mg. The collection of timed urine samples is required for the diagnosis of early nephropathy. One way of collecting is the 24-hour urine for microalbumin. However, there are wide variations in the amount of albumin that is excreted in that period of time. Upright posture, protein ingestion, and exercise all tend to increase urine albumin excretion. For all these reasons, a more accurate method to detect microalbuminuria is to do a morning spot urine for albumin/creatinine. Patients should be instructed to discard a voided urine sample before going to bed and then collecting urine samples thereafter until the morning. When the value is 30 to 300 mg albumin/per gram of creatinine, microalbuminuria is present. However, this test needs to be repeated 2 to 3 times for a duration of 3 to 6 months to confirm the diagnosis.
The prevention of the progression of diabetic nephropathy once it is found can be accomplished by tight glycemic control, a low protein diet (0.8 g/kg/day), and initiation of angiotensin-converting enzyme (ACE) inhibitors. ACE inhibitors have been found to slow the progression of proteinuria, even in normotensive diabetics. This patient's glycemic control is nearly optimal and should be maintained to keep the HgbA1c approximately 7.0% by weight loss, as well as adjusting the insulin regimen. Although all these measures will be beneficial in reducing proteinuria, a diagnosis first needs to be made.