Proteinuria and Microalbuminuria
Proteinuria is the most important early predictor of renal injury by current standards. As with the Ccr, 24-h urine collections to evaluate total protein excretion has been replaced in pediatric practice with random urine total protein:creatinine (Upr/cr) and urine albumin:creatinine (Ualb/cr) ratios. Multiple studies in adults and children have validated the use of randomly voided samples to estimate the total protein excretion in individuals.[108,109] Normal proteinuria is defined as an excretion of less than 150 mg/day of total protein and less than 30 mg/day of albumin. In children, normal proteinuria is reflected by a random Upr/cr less than or equal to 0.2 mg/mg while nephrotic range proteinuria is greater than or equal to 2.0 mg/mg, respectively.[108,109] These ratios are consistent with a daily protein excretion of less than 100 mg/m2/day and more than 1000 mg/m2/day.[108,109] It is important to note that the routine urinalysis used in the pediatrician's office practice cannot estimate daily protein excretion. Urinary dipsticks detect only albuminuria at a concentration in excess of 300 mg/dl. Moreover, low molecular-weight proteinuria, which is the non-albumin component of proteinuria, cannot be detected by the urinary protein dipstick and requires quantitation by the urine total protein method.[108,109] Although less studied in adults, the non-albumin component of proteinuria is frequent in pediatric patients, particularly those with congenital renal disease and interstitial nephropathies. This may be especially important in obese patients who frequently present with heavy proteinuria, normal serum proteins and the absence of edema, suggesting a unique mix of proteinuria that may be dominated by non-albumin proteinuria.
Pediatr Health. 2009;3(2):141-153. © 2009 Future Medicine Ltd.