Kinetics of 125I-beta 2-microglobulin turnover in dialyzed patients

The kinetics of beta 2-microglobulin (beta 2m) were studied in 17 anephric or functionally anephric hemodialyzed patients and five healthy subjects as controls. Highly purified beta 2m was radiolabeled with 125I and infused into patients. The radioactivity in plasma and dialysis fluids was measured during a week including two or three dialysis sessions. Patients were classified in four groups according to treatment: hemodialysis on Cuprophan (N = 5) or on AN69 membranes (N = 5), hemofiltration (N = 4) and CAPD (N = 3). Plasma activity was fitted to a three compartment model. In controls almost 100% of the radioactivity was recovered in urine within 96 hours and there was no extrarenal catabolism. In patients the fractional catabolic rate ranged from 0.0008 to 0.0022 min-1 versus 0.026 to 0.047 min-1 in controls. The synthetic rate was within the range of values from controls in 10 patients but higher in the seven others. It was correlated with plasma beta 2m concentration. Kinetic data indicate a retention of intact beta 2m. The original model was therefore modified with an additional compartment representing beta 2m captation. The amount of capted beta 2m was more elevated in hemodialyzed patients than in patients treated by hemofiltration or CAPD, in whom it could reach 5 mg/kg/day. Hemofiltration or CAPD may eliminate about 30 to 100% of beta 2m produced and therefore contribute to the low captation amount of these patients, as compared with that of patients treated by hemodialysis.