Definition Tests of renal tubular function used to differentiate pre-renal from tubular injury (acute tubular necrosis) test urinary concentrating ability. The normal tubular response to pre-renal conditions is to concentrate the urine for the perceived dehydration, thus maximizing water reabsorption. Urine osmolality is concentrated to over 450 mOs/kg compared to normal serum levels of 280-300 […]