A Single Sample Method for Evaluating 51Chromium-Ethylene Diaminic Tetraacetic Acid Clearance in Normal and Hyperthyroid Cats.

Background: Chronic kidney failure is frequently seen in middle-aged and elderly cats. ⁵¹Chromium-ethylene diaminic tetraacetic acid (⁵¹Cr-EDTA) clearance and single blood sample (SBS) method are used in several species to estimate the glomerular filtration rate (GFR). Hypothesis: The hypothesis of this study was that ⁵¹Cr-EDTA clearance could be determined using an SBS method in normal and hyperthyroid cats. Animals: Forty-six cats were included in this study, with an average age of 9.5 years. Of these cats, 27 had hyperthyroidism; 19 were healthy. Methods: After IV injection of ⁵¹Cr-EDTA (average dose: 4.25 MBq), 7 blood samples were obtained between 5 and 240 minutes. Reference clearance was calculated in mL/min and mL/min/kg body weight, using a 2-compartment model. Optimal time for clearance measurement with SBS was then determined by systematically comparing each individual plasma concentration to the reference multisample clearance. Results: The average reference plasma clearance of ⁵¹Cr-EDTA for all cats was 14.9 mL/min (3.7 mL/min/kg). The clearance in hyperthyroid cats averaged 16.4 mL/min (4.3 mL/min/kg) and in normal cats averaged 10.3 mL/min (2.4 mL/min/kg). The optimal time for the SBS was 48 minutes after injection of tracer ⁵¹Cr-EDTA ( R²= 0.9414), giving the following converting equation: clearance = (0.0066 × DV_{48 minutes}) – 0.9277 (in mL/min). Conclusions and Clinical Importance: In this study, the single sample ⁵¹Cr-EDTA clearance method was used to estimate the global GFR in cats. The method identified differences in clearance between normal and hyperthyroid cats. The optimal time for an SBS was 48 minutes. [ABSTRACT FROM AUTHOR]