Relationship of selected clinical renal function tests to glomerular filtration rate and renal blood flow in cats.

Results of 3 clinical tests of renal function--urine concentrating ability and disappearance of plasma phenosulfonphthalein (PSP) and sodium sulfanilate (SS) were compared with those of 2 classic tests, glomerular filtration rate (GFR) and renal blood flow (RBF), in 11 cats before and after reduction of renal mass. Values (mean +/- SD) obtained from normal cats were maximum urine concentration of 2,270 +/- 407 mOsm/kg (specific gravity values of 1.067 +/- 0.015); T 1/2 for plasma disappearance of PSP of 24.27 +/- 3.5 minutes; T 1/2 for plasma disappearance of SS of 44.42 +/- 5.67 minutes; GFR of 2.94 +/- 0.32 ml/min/kg; and RBF of 10.61 +/- 1.71 ml/min/kg. After reduction of renal mass by vascular ligation and nephrectomy, the cats became azotemic and had significant decreases in GFR and RBF (P less than 0.005), but still were able to concentrate urine to a considerable extent. Both maximum urine concentration and PSP plasma decay were poorly correlated with GFR (r = 0.4060 and 0.3694, respectively) and RBF (r = -0.3439 and -0.3427). Sulfanilate half-life had better correlation with GFR (r = -0.7004) than with RBF (r = -0.5716). Both GFR and RBF increased significantly (P less than 0.005) between postsurgical weeks 1 and 9. It was concluded that experimental cats with azotemia retain considerable ability to concentrate urine and that the SS test is superior to both the PSP test and urine concentration test for clinical estimation of renal function.