Comparison between the renal clearance of endogenous creatinine and inulin in the sheep

Simultaneous renal clearances of inulin and endogenous creatinine were determined during inulin infusions in sheep. The calculated regression of creatinine on inulin clearance differed significantly from the expected line. Discrepancies might be explained by absorption and secretion of creatinine under differing conditions, but it is suggested that lack of specificity of the method used for creatinine determination is an equally likely cause. As the difference between the two clearances was not great (within the range 14 to 48 ml min-1 it was not significant at P less than 0.05), creatinine clearance remains a useful indicator of glomerular filtration. For greatest accuracy, however, inulin clearance remains the method of choice.