Assessment of renal function by 51Cr-EDTA and endogenous creatinine clearances in the pig

In anaesthetized pigs, clearances of 51Cr-EDTA (EDTA) and endogenous creatinine were compared with renal clearance of inulin measured during constant infusion after bolus injection. Creatinine was determined by enzymatic (Kodak Ektachem) as well as conventional (Jaffé) methods. In saline-loaded pigs, renal clearance of constantly infused EDTA was 97.0 +/- 6.7 mL min-1 and identical to the clearance of inulin (94.1 +/- 9.1 mL min-1). There was good agreement between individual clearances. The extraction fractions of the two markers were indistinguishable (0.26 +/- 0.02 and 0.28 +/- 0.03, respectively). In other experiments the clearance of EDTA calculated from the first 4 h of the time course of the plasma concentration after single injection was 64.4 +/- 3.7 mL min-1, correlating well with inulin clearance (63.0 +/- 1.2 mL min-1). When calculated only from the monoexponential phase of the disappearance curve ('slope clearance'), significantly higher results were obtained (+33%, P < 0.001). Renal clearance of EDTA after single injection was 7.5 +/- 1.5 mL min-1 (approximately 12%) lower than inulin clearance (P < 0.001). Values of creatinine clearances determined by the two analytical methods showed a poor agreement with inulin clearance. It is concluded that, in pigs, glomerular filtration rate may be estimated by the clearance of EDTA using constant infusion or single injection of EDTA and that the renal clearance of endogenous creatinine is a less useful a measure of GFR.