Binding of 99Tcm sulphur colloid to blood components: implications in renal transplant rejection

The percentage binding of 99Tcm sulphur colloid to blood components (formed elements and plasma proteins) was studied within 1 min of the intravenous injection of the radiopharmaceutical in humans as well as rats. In humans, 68% of the total blood counts were bound to the formed elements (erythrocytes, leucocytes and platelets). The binding pattern (as percentage of plasma counts) among the plasma protein fractions in humans was as follows: albumin, 9.85 +/- 2.06; fibrinogen, 56.70 +/- 7.96; and total proteins, 66.55 +/- 7.32. Activity bound to fibrinogen represented 82.3 +/- 9.1% of the total protein-bound activity in humans. In rats as well fibrinogen was the predominant binding protein (73.8 +/- 5.6). The significant binding of the 99Tcm sulphur colloid to plasma fibrinogen and formed elements of blood may be one of the reasons for the uptake of this radiocolloid in renal transplants before rejection.