ASSESSMENT OF RENAL-FUNCTION BY CR-51-EDTA AND ENDOGENOUS CREATININE CLEARANCES IN THE PIG

In anaesthetized pigs, clearances of Cr-51-EDTA (EDTA) and endogenous creatinine were compared with renal clearance of inulin measured durin g constant infusion after bolus injection. Creatinine was determined b y enzymatic (Kodak Ektachem) as well as conventional (Jaffe) methods. In saline-loaded pigs, renal clearance of constantly infused EDTA was 97.0 +/- 6.7 mt min(-1) and identical to the clearance of inulin (94.1 +/- 9.1 mi min(-1)). There was good agreement between individual clea rances. The extraction fractions of the two markers were indistinguish able (0.26 +/- 0.02 and 0.28 +/- 0.03, respectively). In other experim ents the clearance of EDTA calculated from the first 4 h of the time c ourse of the plasma concentration after single injection was 64.4 +/- 3.7 mt min(-1), correlating well with inulin clearance (63.0 +/- 1.2 m t 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 mt min(-1) (similar to 12%) lower than inul in clearance (P < 0.001). Values of creatinine clearances determined b y the two analytical methods showed a poor agreement with inulin clear ance. 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 creatinin e is a less useful a measure of GFR.