Aim: We have studied 160 children with a variety of renal diseases, 14 of them with chronic renal failure (CRF), to evaluate maximum urinary osmolality as a predictor of glomerular filtration rate (GFR) testing the hypothesis that a normal GFR is necessary to have a normal urinary concentrating capacity.
Methods: All patients had a serum creatinine measured. GFR was calculated according to the Schwartz formula. All patients underwent desmopressin (DDAVP) test to evaluate renal concentrating capacity.
Results: Patients with CRF were unable to concentrate the urine beyond 486 mosm/kg whereas all patients with a normal concentrating capacity (urine osmolality >835 mosm/kg) had a normal GFR. Desmopressin test sensitivity to detect CRF was 100% and specificity 70.5%. A significant negative correlation was found between urinary osmolality after DDAVP administration and serum creatinine levels and between urinary volume corrected by 100 mL of GFR (V/GFR) and urinary osmolality.
Conclusion: In our series, a normal concentrating capacity was always associated with a normal GFR while all patients with decreased GFR had a concentrating capacity defect. Thus, in the evaluation of infants and children with renal disease, the finding of a normal urinary concentrating capacity will suggest and intact glomerular and tubular function.