PLASMA-CLEARANCE OF NONRADIOACTIVE IOHEXOL AS A MEASURE OF GLOMERULAR-FILTRATION RATE

Renal clearance of inulin is the best available indicator of GFR but c annot be used routinely for clinical purposes and is also difficult to perform for clinical investigation when repeated measurements are req uired, The aim of this study was to find a reliable alternative to inu lin clearance that would allow one to avoid the use of radioactivity a nd problems related to the continuous infusion of the marker. The plas ma clearance of unlabeled iohexol, a nonionic contrast agent, was used . Forty-one patients (creatinine clearance 6 to 160 mL/min per 1.73 m( 2)) underwent simultaneous measurements of renal clearance of inulin a nd plasma clearance of iohexol. Iohexol was given as a single iv dose, and blood samples were drawn up to 600 min after the administration. Iohexol concentrations (by HPLC) were analyzed by a two-compartment, o pen-model system. A highly significant correlation between the plasma clearance of iohexol and the renal clearance of inulin over a wide ran ge of GFR values was found. By analyzing the data with a simplified me thod that uses a one-compartment model corrected with the Brochner-Mor tensen formula, an excellent correlation with the inulin clearance was also observed. When only patients with moderate to severe renal failu re were considered, a significant correlation between the two methods was found, A further comparison between GFR determined with iohexol an d iopromide, a new low-osmolarity, low-viscosity contrast medium, was also performed in a subgroup of patients. A highly significant correla tion between the plasma clearance of iohexol and iopromide over a wide range of GFR values was found. These findings indicate that the propo sed method of measuring GFR by the plasma clearance of unlabeled iohex ol or iopromide is a good alternative to the inulin clearance techniqu e.