Relationship between plasma iohexol clearance and urinary exogenous creatinine clearance in dogs

The objective of this study was to determine if plasma iohexol clearance, c omputed by a 1-comparmrent model defined by 3 plasma samples, was an accura te measure of glomerular filtration rate (GFR) in dogs. Twenty-two adult Be agle dogs of both genders were studied;Ten dogs bad intact kidneys, and 12 dogs had surgically reduced renal mass. A bolus injection of iohexol was ma de, and blood was obtained for plasma iohexol assay after 120, 180, and 240 minutes. Plasma was analyzed for iohexol concentration by means of 3 assay methods: chemical, high-performance liquid chromatography (HPLC), and indu ctively coupled plasma emission spectroscopy (ICP). Urinary clearance of ex ogenous creatinine was used to measure GFR for three 30-minute periods occu rring between 150 and 240 minutes after iohexol injection. Plasma clearance of iohexol and renal clearance of creatinine were compared by linear regre ssion analysis and by limits of agreement techniques, plasma iohexol cleara nce and urinary exogenous creatinine clearance were significantly correlate d (chemical R-2 = .90; HPLC R-2 = .96; and ICP R-2 = .96). The l-compartmen t iohexol clearance:exogenous creatinine clearance ratios were 1.04 +/- 0.1 7, 1.05 +/- 0.14, and 1.10 +/- 0.15 for the chemical, HPLC, and ICP methods of assay, respectively, indicating that plasma iohexol clearance slightly overestimated GFR. Assuming a +/- 2 standard deviation interval for error c orrected plasma iohexol clearance measured GFR with +/- 34% accuracy for th e chemical, +/- 26% accuracy for the HPLC, and +/- 21% accuracy for the ICP method. These results indicate that plasma iohexol clearance should have u tility for detection of renal dysfunction earlier in the course of progress ive renal disease than is possible with measurement of plasma creatinine or urea concentrations.