Comparison of four methods of estimating glomerular filtration rate in cats
Rogers, K.S.; Komkov, A.; Brown, S.A.; Lees, G.E.; Hightower, D.; Russo, E.A.
American Journal of Veterinary Research 52(6): 961-964
1991
ISSN/ISBN: 0002-9645 PMID: 1883102 Document Number: 375377
Four methods of evaluating renal function were performed in 6 cats anesthetized with halothane in oxygen. Glomerular filtration rate (GFR) was measured simultaneously in each cat by exogenous creatinine clearance (ECC), bolus inulin clearance, and 99mTc(Sn)-diethylene-triaminepentaacetic acid (DTPA) clearance determined by 2 different methods. In the first DTPA clearance method (DTPA-1), we measured radioactivity in serial blood specimens to construct plasma disappearance curves for calculation of GFR. In the second DTPA clearance method (DTPA-2), we used serial external head counts of radioactivity and a single blood specimen to construct plasma disappearance curves for calculation of GFR. Bolus inulin clearance was calculated from plasma disappearance curves using a 1-compartment open pharmacokinetic model (IN-1) and a 2-compartment open pharmacokinetic model (IN-2). Glomerular filtration rates were measured over 3 hours, for creatinine and DTPA methods, and over 4 hours for the inulin methods. The GFR obtained with the reference method (ECC) was 2.56 .+-. 0.61 ml/min/kg of body weight (mean .+-. SD). Values for GFR determined by ECC and DTPA-1 were significantly correlated (r = 0.852; P .ltoreq. 0.05). Correlation between ECC and DTPA 2 was not as good (r = 0.783; P .ltoreq. 0.10), but the 2 DTPA methods significantly correlated with one another (r = 0.897; P .ltoreq. 0.05). Regardless of the method of calculation, bolus inulin clearance was poorly correlated with ECC (IN-1: r = 0.538, P .gtoreq. 0.10; IN-2: r = 0.430, P .gtoreq. 0.10) and DTPA-1 IN-1: r = 0.601, P .gtoreq. 0.10; IN-2: r = 0.625, P .gtoreq. 0.10). The 2 methods of calculating inulin clearance were highly correlated (r = 0.927; P .ltoreq. 0.01). The DTPA clearance calculated from directly measured plasma disappearance curves (DTPA-1) compared favorably with ECC as an estimate of GFR and appears to be a safe, reliable, and less invasive method of determining GFR in cats.