The important clinical review by Sheldon Tobe and colleagues1 reinforces the value of random testing of urine specimens in determining the albumin–creatinine ratio for the diagnosis of diabetic nephropathy, as recommended by the 1998 Canadian clinical practice guidelines for diabetes.2 However, the authors did not mention the challenge of applying these recommendations to adolescents and young adults.
The new diabetes care guidelines being developed for publication in 2003 contain a separate section regarding children and adolescents because of the unique aspects of diagnosis, care and surveillance in youth. One major challenge is the interpretation of microalbuminuria in adolescents.
Approximately 5% of healthy adolescents and 70% to 80% of all children and adolescents investigated for proteinuria have benign orthostatic proteinuria,3 excreting up to 1.5 g protein per day without hematuria or edema. Thus, adolescents with diabetes will have false-positive results for microalbuminuria according to the definition of greater than 30 mg/d in a timed collection or greater than 2.0 mg/mmol in males and greater than 2.8 mg/mmol in females in random urine samples for albumin–creatinine ratio.
Routine surveillance of renal function in youth with type 1 diabetes at 15 years of age requires a first morning urine sample for determination of albumin–creatinine ratio or a timed overnight urine collection to calculate albumin excretion rate. It is vital that adolescents void before going to bed so that the first morning urine sample represents urine produced in the recumbent position. Microalbuminuria is confirmed when results are abnormal in 2 of 3 first morning urine samples on consecutive days.4 Even with careful sample collection, the natural history of microalbuminuria in adolescents with type 1 diabetes is variable: approximately one-third of cases of microalbuminuria resolve spontaneously, one-third of cases involve stable but persistent microalbuminuria with no progression to macroalbuminuria, and one-third of cases progress to macroalbuminuria and overt diabetic nephropathy.5
A second problem is the greater prevalence of primary renal disease in populations at risk for type 2 diabetes mellitus. The risk of congenital and acquired renal disease is 4.5-fold and 6.1-fold greater respectively in First Nations children than in the general pediatric population in Manitoba.6 Specifically, the prevalence of IgA nephropathy is 10-fold greater in First Nations children in Manitoba.7 IgA nephropathy is also greater in Aboriginal people in Australia and the United States.8 Therefore, it is critical to look for evidence of concomitant glomerular disease at the time of diagnosis of type 2 diabetes in adolescents and to actively pursue investigations, including renal biopsy in selected cases of microalbuminuria or macroalbuminuria at presentation, as it is more likely that the underlying diagnosis is nondiabetic nephropathy. The high morbidity associated with end-stage renal disease in young adults with type 2 diabetes diagnosed in childhood demands our careful attention.9
Heather Dean Elizabeth Sellers Section of Pediatric Endocrinology Patricia Birk Tom Blydt-Hansen Malcolm Ogborn Section of Pediatric Nephrology Department of Pediatrics University of Manitoba Winnipeg, Man.