CLEARANCE OF I-131 BY HEMODIALYSIS

There are no available data documenting the dialysis clearance of iodide in humans. This work quantitates the hemodialysis clearance of iodide (as I-131) over time and examines certain factors which influence that clearance. In a single-patient study, three dialysis periods were studied over the 24 to 96 hours following administration of 129 mCi I-131 given as (NaI)-I-131. Hemodialysis clearance of I-131 was calculated both from the arterio-venous difference of I-131 across the artificial kidney and the appearance of I-131 in the expended dialysate. Calculations were based on I-131 activity in whole blood, whole plasma, and the supernate of plasma treated with 10% trichloroacetic acid (TCA). The hemodialysis clearance of I-131 was highest when calculated from the activity of the plasma supernate, 171.3 +/- 6.0 ml/min for the period 24-29 h. post dosing, and fell in a linear fashion with time. The clearance calculated from whole blood activity was always intermediate to that from whole plasma (lowest) or the plasma supernate (highest). The percentage of plasma I-131 activity precipitated by TCA rose over the study period and displayed a strong negative correlation to the hemodialysis clearance of I-131. The hemodialysis clearance of iodide, as I-131, is on the order expected for a free ion and is 4-5 times higher than the endogenous renal clearance of the ion. However, the calculated clearance varies with respect to total time of dialysis and the fraction of blood in which the I-131 activity is measured. In both cases, deviations from the initial clearance values likely result from overestimation of the diffusible ion due to an increasing fraction of protein-associated, non-diffusible iodide. After a period of time which allowed the therapeutic uptake of I-131 into neoplastic thyroidal tissue, hemodialysis efficiently cleared the remaining dose of I-131 given this patient, reducing the radiation exposure of non-thyroidal tissues. The use of hemodialysis in patients with compromised renal function who require I-131 therapy deserves further consideration.