Simplified methods for estimation of Tc-99m-pentetate and I-131-orthoiodohippurate plasma clearance in dogs and cats

The purpose of this study was to evaluate simplified methods for estimation of Technetium Tc 99m (Tc-99m)-pentetate and orthoiodohippurate I 131 (I-13 1-OIH) plasma clearance in dogs and cats with 1 and 2 blood samples. Plasma clearances were calculated after a bolus injection of 1.85-11.1 MBq of Tc- 130-pentetate and I-131-OIH with a 2-compartment model based on a 12-point curve as a reference method in 21 dogs and 18 cats. Three 2-sample and 3 si ngle-sample methods were investigated. The method yielding the smallest sta ndard deviation of the difference between the reference method and the simp lified method was selected as the optimal one. Linear regression analysis w as performed between the reference method and tilt: simplified method and c oefficient of determination (R-2) was calculated. Fur Tc-130-pentrlatr plas ma clearance. die optimal 2-sample method was the one with a mono-compartme nt model with samples taken at specific times. For I-131-OIH plasma clearan ce. the estimation was improved slightly by raising the clearance calculate d with a monocompartment model to the power of an empirically determined pa rameter The optimal single-sample method was the one with a linear quadrati c regression between the volume oi distribution oi the tracer at 1! specifi c time and the clearance calculated with 12 samples. Two-sample methods per formed significantly better than did single-sample methods. The conclusion is made that Te-99m-pentetate and I-131-OIH plasma clearances can be estima ted in dogs and cats with 1 or 2 blood samples With a reasonable margin of error compared to plasma clearances calculated with a 2-compartment model a nd 12 blood samples.