DETERMINATION OF RESIDUAL RENAL-FUNCTION WITH IOHEXOL CLEARANCE IN HEMODIALYSIS-PATIENTS

Residual renal function (RRF) may contribute significantly to the tota l dialysis prescription. Conventional quantitation of RRF in hemodialy sis (HD) patients is measured by urea clearance and requires a 24-hour urine collection which is often difficult to perform and inaccurate. The renal clearance of iohexol was evaluated as an alternative method for RRF assessment (iohexol-derived RRF) in hemodialysis patients. An intravenous bolus of iohexol (12 ml; 300 mg iodine/ml) was administere d to 42 hemodialysis patients following routine HD. A single blood sam ple was obtained approximately 44 hours later (pre-HD) to determine th e plasma clearance of iohexol using x-ray fluorescence methods. Total body clearance of iohexol (C-TBio) and non-renal clearance of iohexol (C-NRio) 2.87 +/- 0.3 ml/min (mean +/- SEM) were used to calculate ioh exol-derived RRF (C-TBio - C-NRio). Iohexol-derived RRF determinations were then compared to urea clearance-derived RRF measurements. The RR F contribution to the dialysis prescription was also calculated utiliz ing iohexol-derived RRF compared to urea-derived RRF. Iohexol-derived RRF did not differ from urea-derived RRF (2.48 +/- 0.3 vs. 2.64 +/- 0. 4 ml/min, P = 0.21). The RRF contribution to the weekly dialysis presc ription (Kt/V) did not differ when iohexol-derived RRF was compared to urea-derived RRF (0.94 +/- 0.1 vs. 0.93 +/- 0.1, P = 0.9). Additional ly, the effect of iohexol on RRF was assessed in 17 HD patients. Urea- derived RRF determinations one week after iohexol exposure did not dif fer from those measured one week prior to iohexol exposure (3.17 +/- 0 .6 vs. 2.91 +/- 0.5 ml/min, respectively). Thus, renal clearance of io hexol can be an accurate and safe measure of RRF in HD patients and po tentially simplify delivery of the dialysis prescription.