The kinetics of short-lived indium-111 radiolabelled platelets

We have studied the kinetics of autologous 111In-labelled platelets in patients with reduced platelet life span (less than 4.5 d), most of whom were thrombocytopenic, and of homologous 111In-labelled platelets in patients with severe thrombocytopenia. Intrasplenic platelet transit time (t) was calculated by compartmental and deconvolution analysis. In patients with a mean platelet life span of less than a few h, compartmental analysis may not be valid and so only deconvolution analysis was applied. There was a close correlation between values of t given by the two approaches (r = 0.88, n = 18, P less than 0.001). In some patients with severely reduced mean platelet life span (MPLS), the deconvolved splenic platelet clearance curves appeared to approach an asymptote, the relative magnitude of which was indicative of the irreversible extraction fraction by the spleen of incoming platelets. In other patients with severely reduced MPLS resulting from abnormal intra-hepatic platelet destruction, the deconvolved splenic curves resembled the normal. The intrasplenic platelet transit time showed no clear relationship with other parameters. It was concluded that platelet pooling within the spleen is normal in patients with reduced platelet life span, including idiopathic thrombocytopenic purpura, even when the predominant site of destruction is the spleen, and that platelets are not delayed in transit through the spleen in preparation for their removal from the circulation and ultimate destruction.