ESTIMATION OF GLOMERULAR FILTRATION RATE IN KIDNEY TRANSPLANT RECIPIENTS BY IOHEXOL CLEARANCE - COMPARISON WITH INULIN CLEARANCE AND CREATININE CLEARANCE EQUATIONS.

P346 Aims: glomerular filtration rate (GFR) can be determined exactly by measuring the clearance of an ideal filtration marker, such as inulin. The classic method of measuring inulin clearance includes constant intravenous infusion and timed collections of urine. In order to avoid the need for timed urine collections, iohexol has been used as a filtration marker. In non transplanted patients, good agreement has been shown for GFR determined by the classic inulin clearance and by the iohexol plasma clearance. The aim of this study was to validate iohexol clearance compared with inulin clearance in a population of kidney allograft recipients and to compare this approach with some published equations for determination of creatinine clearance. Patients and methods: thirty two kidney transplant recipients with stable graft function (creatininemia between 69 and 330 μmol/) were evaluated by both inulin and iohexol clearances. The patients underwent simultaneous measurements of renal clearance of inulin and plasma clearance of iohexol. Iohexol was given as a single IV dose (Omnipaque 300, 5 ml), and blood samples were drawn at 120, 150, 180, and 210 for patients with estimated clearance above 40 ml/min, and 240 and 270 minutes if estimated clearance was below 40 ml/min. Iohexol concentrations were analyzed by a one-compartment model corrected by the Brochner-Mortensen formula. Agreement between methods was evaluated by linear regression and according to Bland and Altman analysis. Results: We found excellent correlation (r=0.97; r2=0.95) and a good agreement between inulin clearance and iohexol clearance. Iohexol determination with four blood samplings (120, 150, 180 and 210 min) is sufficient in a large range of renal function. Moreover, predicted equations are inaccurate for precise estimation of DFG when compared to inulin clearance (Cockcroft and Gault: r2 = 0.82, Nankivell: r2 = 0.77, MDRD2: r2 = 0.60, Jellife: r2 = 0.40, Walser: r2 = 0.66). Conclusion: Simplified method using 4 points iohexol clearance and avoiding urine collection is a reliable method of determination of GFR in kidney transplanted patients and can be used for measuring GFR in multicenter clinical trials where GFR is required as a major endpoint even among patients with altered renal function.