Evaluation of Tc-99m-DTPA for renal clearance studies in the pig

Conventional creatinine clearance studies in the pig are complicated by difficulties with catheterisation, infection, accurate collection and active creatinine renal tubular reabsorption. We compared a single injection, 99mTc-DTPA elimination method with creatinine clearance. Nineteen pairs of GFR estimations were performed in 10 pigs: 7 in normal pigs and 12 following bile duct ligation and/or nephrectomy. Red cell and plasma protein binding of the isotope and its hepatobiliary excretion was assessed. Absolute and weight normalised endogenous creatinine clearances correlated significantly with 99mTc-DTPA elimination. 99mTc-DTPA red cell binding and hepatobiliary excretion were negligible. Thus, 99mTc-DTPA elimination is a valid indicator of changes in renal function in grouped porcine studies, particularly in the biliary obstruction model. However, isotope plasma protein binding was high in the 2 normal pigs assessed. Individual accuracy would be improved by routine protein binding correction, unless consistently low for a particular preparation.