Association between fever and reduced renal concentrating capacity

The renal concentrating capacity was assessed in 18 adult patients with febrile infections of non-renal origin. Urine osmolatity was determined after overnight fluid deprivation for 10 hours followed by subcutaneous administration of 4 micrograms of desmopressin. All patients had a transient reduction of the concentrating capacity as compared to a subsequent test performed one month later (p less than 0.001). During the febrile disease, 12 of 18 patients could not achieve a maximal urine osmolality above the lower limit (-2 SD) of an age-related reference interval. These results suggest that in febrile patients with bacteriuria, a reduced renal concentrating capacity does not necessarily mean that the infection is localised to the kidneys but may rather be explained by fever per se.