Plasma Clearance of Exogenous Creatinine, Exo-Iohexol and Endo-Iohexol in Healthy Cats, Cats with Hyperthyroidism and Cats with Chronic Kidney Disease
Measurement of glomerular filtration rate (GFR) in cats allows detection of a decreased kidney function in an early stage of kidney disease. The plasma clearance of exogenous creatinine (PECCT) seems to be a promising alternative to the more complicated methods for GFR measurement in cats. The objective of this study was to compare PECCT, exo-iohexol (Pex-ICT) and endo-iohexol (Pen-ICT) for discriminating healthy cats (H), hyperthyroid cats (HT) and cats with chronic kidney disease (CKD) suspected to have respectively normal, high and low GFR values.
Inclusion criteria for the H cats were no clinically significant abnormalities on clinical exam and blood and urine analysis. Cats with HT were included with clinical signs compatible with hyperthyroidism, increased total thyroxin serum concentration and increased thyroidal uptake of 99mTcO4-. Antithyroid drugs had been discontinued at least 3 weeks prior to inclusion. Cats with CKD were included based on symptoms of CKD and azotemia (IRIS stage II or higher). The PECCT, Pex-ICT and Pen-ICT were performed in a combined manner (described by van Hoek et al., JVIM 2007;21:950-958). A linear mixed model was used for statistical analysis. Results are expressed as mean ± sd.
The study included 6 H cats (age 7-12 months, BW 4.3-5.6 kg), 6 HT cats (age 8-16 years, BW 2.6-6.2 kg) and 4 CKD cats (age 10-13 years, BW 4.5-6.6 kg). Plasma clearance values (ml/min/kg) for the Pex-ICT, Pen-ICT and PECCT respectively are 1.8 ± 0.3, 3.1 ± 0.6 and 2.8 ± 0.5 in the H cats, 4.1 ± 1.2, 4.3 ± 1.2 and 4.7 ± 1.2 in the HT cats, and 0.9 ± 0.2, 0.9 ± 0.1 and 1.0 ± 0.1 in the cats with CKD. There was a significant difference between Pex-ICT and Pen-ICT (P<0.001) and PECCT (P<0.001) but not between Pen-ICT and PECCT (P=0.210) in H cats. However, there was no significant difference between GFR methods in cats with CKD (P=0.386) or HT cats (P=0.185). There was a significant difference between CKD cats and HT cats for Pex-ICT (P<0.001), Pen-ICT (P<0.001) and PECCT (P<0.001), between H and HT cats for Pex-ICT (P=0.001), PECCT (P=0.005) but not for Pen-ICT (P=0.067), and between CKD and H cats for Pen-ICT (P=0.004), PECCT (P=0.018) but not for Pex-ICT (P=0.280).
The Pex-ICT, Pen-ICT and PECCT do not differ between each other in cats with low or high GFR values. However, there is a significant difference in cats with normal GFR values. The Pex-ICT and Pen-ICT can detect the large difference between low and high GFR values. However, Pex-ICT cannot detect the smaller difference between normal and low GFR values, and Pen-ICT cannot detect the smaller difference between normal and high GFR values. The PECCT is able to detect a significant difference in GFR between H, HT and CKD cats. This supports the hypothesis that the PECCT is valuable to detect a decreased kidney function.