Absence of renal sodium adaptation in chronic renal failure

A patient with advanced chronic renal failure secondary to polycystic kidney disease suffered an episode of volume contraction during which his urinary sodium concentration fell to less than 5 mEq daily. Urine sodium excretion remained at this level when later in his course he became clinically volume expanded. The patient also suffered from Crohn's disease and had an ileostomy from which he excreted from 100 to 150 mEq sodium daily. We propose that this patient's capacity to produce urine virtually free of sodium despite advanced renal failure was a result of the persistent loss of sodium from his ileostomy. This sodium loss obviated the development of the adaptive natriuresis that usually occurs in the functioning nephrons of the diseased kidney and prevented the development of a 'salt-losing' tendency.