Evaluation of single-injection method of inulin and creatinine as a renal function test in normal cats

A single injection method for estimating glomerular filtration rate (GFR) by measuring plasma inulin and creatinine clearances was evaluated in 10 healthy cats. GFRs were estimated from the plasma clearance (PC) by dividing the injected dose of an indicator by the area under the plasma disappearance curve (AUC). AUC was determined by 2 common pharmacokinetic analyses, the two-compartment model and the trapezoidal rule. AUCs determined by these two methods were significantly correlated both in inulin (r = 0.993) and creatinine (r = 0.959). To minimize errors, GFR was estimated by PC only if AUC/10 was greater than the area under the curve from the final sampling time to infinitive (A2). GFRs determined by PC of inulin at final sampling time of 180 and 240 min were 3.61 +/- 0.64 and 3.63 +/- 0.67 ml/min/kg of body weight (mean +/- SD), respectively. These values corresponded to the reference range reported for normal cats. In contrast, when creatinine was used as a maker, A2 was always greater than AUC/10 at any final sampling time and GFRs estimated using these AUCs of creatinine were significantly greater than those of inulin, suggesting creatinine may not be suitable indicator for the single injection method.