Renal function in acute febrile urinary tract infection in children: pathophysiologic aspects on the reduced concentrating capacity.

In an attempt to elucidate the reduced concentrating capacity in acute pyelonephritis, we studied the renal function in 14 children, 5 to 16 years of age. Clearance of inulin, PAH, and free water, urinary sodium excretion, and maximal urine osmolality after 18 hours of thirst have been determined at and within 10 months after infection. Glomerular filtration rate and renal plasma flow were found to be increased during infection and normalized after infection. Urinary sodium excretion, distal sodium delivery, and maximal urine osmolality were decreased during infection and increased afterwards. Kidney size was also increased during infection. It is postulated that the reduced concentrating capacity is due to a washout effect mediated by an increased medullary blood flow and to a low distal tubular sodium delivery.