Platelet survival determined with 51Cr versus 111In.

Optimal labelling conditions of human platelets with 111In-oxine were determined in vitro. Based on this optimized technique, platelet mean life span (MLS) and platelet sequestration site were comparatively evaluated in 79 patients with two labels, 51Cr (n = 26) and 111In (n = 53). Patients were subgrouped according to clinical criteria as autoimmune thrombocytopenic purpura (AITP) (group 1; n = 49), hypersplenism (2; n = 12), impaired thrombopoiesis (3; n = 3), unclassified thrombocytopenia (4; n = 6), and nonthrombocytopenic patients (5; n = 9). In patients with AITP and hypersplenism the mean values for the MLS determined either with 51Cr or with 111In were lowered but the difference was not statistically significant, neither for group 1 (18.6 h vs 17.3 h; P greater than 0.2) nor for group 2 (94.7 vs 122.3 h; P greater than 0.2). The correlation between MLS and platelet counts in patients with AITP was significant for both labels (P less than 0.001). The 15 min recovery tended to be higher with 111In in all groups, but the difference was significant (P less than 0.05) only for group 1. The sequestration sites were similar with both labels. We conclude that, contrary to previous reports, platelet survival studies yield similar results with both the 51Cr and 111In methods. Due to its distinct advantages 111In is the label of choice for investigation of platelet kinetics.