Glomerular filtration rate in dogs as estimated via plasma clearance of inulin and iohexol and use of limited-sample methods

OBJECTIVE: To compare plasma clearance of inulin and iohexol determined by use of 9 plasma samples for evaluation of glomerular filtration rate in dogs and to evaluate limited-sample approaches for evaluation of plasma clearance of these markers. ANIMALS: 43 dogs of various breeds that weighed between 5.5 and 63 kg and that had various degrees of renal function. PROCEDURES: 9 plasma samples were obtained from each dog at 5 minutes to 6 hours after IV bolus injection of iohexol and inulin. Clearance was calculated by use of results for all 9 samples (ie, reference method). Results for 3 limited-sample strategies for determination of plasma clearance of iohexol and inulin were compared with results for the reference method. RESULTS: Mean clearance of inulin and iohexol for the reference method was 2.72 and 2.48 mL/min/kg, respectively. The mean difference between clearance of these 2 markers for the reference method was 0.24 mL/min/kg. In general, use of the limited-sample strategies yielded clearance values similar to those for the reference method. More accurate estimates of clearance were obtained for iohexol than for inulin by use of the limited-sample methods. CONCLUSIONS AND CLINICAL RELEVANCE: Use of iohexol and inulin yielded similar but not identical results for plasma clearance. Accuracy for limited-sample methods would be acceptable for many clinical and research situations.