ESTIMATION OF GLOMERULAR-FILTRATION RATE IN DOGS WITH TC-99M-DTPA ANDIOHEXOL

The glomerular filtration rates (GFR) of 18 dogs of different breeds w ere estimated by simultaneously comparing the plasma decay curves of ( 99M)-Tc-diethylenetriaminepentaacetic acid (Tc-DTPA) and the contrast medium iohexol. Nine of the dogs were clinically healthy, and nine had renal disease. After the intravenous injection of the two substances, nine to 12 blood samples were taken during the first six hours and in some cases up to 24 hours. The total clearance of the substances was determined by one- and two-compartment models. Individual GFR(iohexol) values, estimated by using a two-compartment model in 16 of the dogs, ranged from 39.0 mi min(-1) m(-2) to 84.3 mi min(-1) m(-2) and for GF R(Tc-DTPA) from 41.1 mi min(-1) m(-2) to 106.6 mi min(-1) m(-2). The G FR(iohexol) values estimated by using a one-compartment model in the 1 8 dogs ranged from 4.52 mi min(-1) m(-2) to 105 mi min(-1) m(-2) and f or GFR(Tc-DTPA) from 5.4 mi min(-1) m(-2) to 118.9 mi min(-1) m(-2). T he agreement between the two methods was good, as shown by a limits of agreement plot. The ratio of GFR(Tc-DTPA)/GFR(iohexol) was 1.15 throu ghout the range of measurement (SD=0.085). The study indicates that th e iohexol method is a valid measure of GFR in the dog. The practical a spects make it a useful tool in small animal practice.