Plasma clearance of exogenous creatinine, exo-iohexol, and endo-iohexol in hyperthyroid cats before and after treatment with radioiodine.
BACKGROUND
Glomerular filtration rate (GFR) can be measured by clearance methods of different markers showing discrepancies and different reproducibility in healthy cats. Studies comparing different methods of GFR measurement in hyperthyroid cats have not yet been performed.


OBJECTIVE
Plasma clearance of exogenous creatinine (PECCT), exo-iohexol (PexICT), and endo-iohexol (PenICT) could lead to differences in GFR measurement and the need to use the same clearance method when comparing GFR before and after radioiodine treatment in hyperthyroid cats.


METHODS
Fifteen client-owned hyperthyroid cats.


METHODS
GFR was measured 1 day before and 1, 4, 12, and 24 weeks after treatment. Intravenous injection of iohexol was followed immediately by IV injection of creatinine. Plasma creatinine was measured by an enzymatic method. Plasma endo- and exo-iohexol were measured by high-performance liquid chromatography coupled to ultraviolet detection.


RESULTS
Globally, the 3 GFR methods resulted in significantly different (P < .001) GFR results. GFR results among the different methods were the same (P= .999) at all time points. All 3 techniques indicated decreasing GFR after (131)I treatment. For each GFR technique, a significant decrease in GFR was observed between time point 0 and all other time points. This decrease stabilized 4 weeks after treatment, with very little decline afterward.


CONCLUSIONS
It is mandatory to use the same GFR technique in follow-up studies. GFR testing at 4 weeks posttreatment could allow assessment of the final renal functional loss after treatment in hyperthyroid cats.
van Hoek
I
I
Department of Medicine & Clinical Biology of Small Animals, Faculty of Veterinary Medicine, University of Ghent, Salisburylaan 133, 9820, Merelbeke, Belgium. ingrid.vanhoek@ugent.be
Lefebvre
H P
HP
Kooistra
H S
HS
Croubels
S
S
Binst
D
D
Peremans
K
K
Daminet
S
S
D000818:Animals; D002371:Cat Diseases / Q000378:metabolism* / Q000532:radiotherapy; D002415:Cats; D003404:Creatinine / Q000493:pharmacokinetics*; D005260:Female; D005919:Glomerular Filtration Rate / Q000662:veterinary; D006980:Hyperthyroidism / Q000378:metabolism / Q000532:radiotherapy / Q000662:veterinary*; D007455:Iodine / Q000627:therapeutic use*; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D007472:Iohexol / Q000493:pharmacokinetics*; D007674:Kidney Diseases / Q000175:diagnosis / Q000662:veterinary; D008297:Male; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D007472:Iohexol; D007455:Iodine; D003404:Creatinine