Kinetics of 131I-β2 microglobulin in hemodialysis patients:: Assessment using total body counting

The kinetics of I-131-beta(2)-microglobulin (beta(2)-M) were studied using external total body gamma counting in a low noise chamber after administration of trace doses of radioactivity (4 mu Ci) in 14 uremic patients treated by either hemodialysis or hemofiltration. Data were collected over a 1 week period that included 3 dialysis sessions. The following artificial membranes were used: Cuprophan, polyacrylonitrile AN69, polysulfone, polymethylmethacrylate (PMMA), and polyamide. Radiolabeled beta(2)-M excretion by an extrarenal route was nearly nonexistent. The I-131-beta(2)-M half-life was between 2.4 and 8 days, shorter in patients with residual diuresis. A mean removal of 153 +/- 33 mg/L of beta(2)-M was obtained per dialysis session with a highly permeable membrane. A hemofiltration session (25 L exchange per session) was slightly more efficient in removing beta(2)-M than a 4 h hemodialysis session with the same AN69 highly permeable membrane. The amounts of I-131-beta(2)-M binding on the membranes, expressed as beta(2)-M equivalents, were 0, 16, 54, 58, and 59 mg/m(2) for Cuprophan, polysulfone, polyacrylonitrile AN69, polyamide, and PMMA, respectively. In conclusion, the decrease of total body gamma counting directly reflected the beta(2)-M breakdown and removal in hemodialysis patients. Intact beta(2)-M was removed by convection with synthetic, highly permeable membranes. In addition, membrane adsorption accounted for 15% (polysulfone) to near 100% (PMMA) of the beta(2)-M removal per session Adsorption was of the same magnitude regardless of the dialysis technique in use, indicating a membrane saturability process. None of the currently available dialysis procedures based on a 3 sessions per week schedule can balance beta(2)-M generation.