EVALUATION OF A SINGLE INJECTION METHOD, USING IOHEXOL, FOR ESTIMATING GLOMERULAR-FILTRATION RATE IN CATS AND DOGS

Objective-To evaluate the utility of a method for estimating glomerula r filtration rate (GFR) after single IV administration of iohexol. Des ign-The plasma clearance of iodine (PCl), taken as the quotient of the administered dose of iodine (300 to 600 mg of I/kg of body weight) di vided by the area under the plasma iodine concentration versus time cu rve determined by 4 methods (PCl1-PCl4). The results for PCl were comp ared with simultaneously obtained values for the urinary clearance of exogenously administered creatinine (CCr), a widely accepted method fo r the measurement of GFR in cats and dogs. Animals-Cats and dogs that were renal intact (n = 5 cats; n = 1 dog) or had renal mass reduced by partial nephrectomy (n = 5 cats; n = 7 dogs). Results-Values for PCl were closely related (R(2) values ranged from 0.947 to 0.992; P < 0.00 01 in all cases) to CCr. Despite this close correlation between CCr an d PCl, the 95% confidence interval for the difference between PCl3 and CCr included values that exceeded 1.4 ml/min/ kg, which represents 50 % of the mean value for CCr in renal-intact cats. Conclusions-Determin ation of PCl provided a reliable estimate of GFR in cats acid dogs of this study. However, differences between 1 of the methods (PCl3) and C Cr are clinically important, emphasizing the need to use more than sim ple linear regression analysis and correlation coefficients when attem pting to validate new measurement techniques. Clinical Relevance-The d etermination of PCI provided a reliable estimate of GFR in cats and do gs of this study.