Platelet radiolabelling with 111 Indium for in vivo studies: a methodological reappraisal.

Two ligands widely used for 111In labeling of human platelets, oxine and tropolone, were compared as to the degree of their influence on platelet function. The labelling efficiency was assessed as a function of experimental variables. A good preservation of platelet function as evaluated by ex vivo aggregation was obtained with both techniques. The extent of tracer detached from platelets was evaluated in vitro and in vivo: in normal subjects 111In was virtually all bound to platelets. A significant reduction in radiolabelling efficiency and a decreased percentage of 111In bound to platelets in vivo was observed in patients with platelet counts < 150,000/mL.