Renal function in cystic fibrosis with special reference to the renal sodium handling.

Renal function was studied in 16 patients with cystic fibrosis, aged 5 to 19 years. The mean glomerular filtration rate and filtration fraction were increased compared to those in controls. Basal urinary sodium excretion as well as renal responses to oral and intravenous sodium loads were low, indicating an increased renal sodium reabsorption. Diluting capacity, measured as free water clearance, was decreased because of a low distal sodium delivery which might indicate an increased proximal sodium reabsorption.