Comparative studies of the in vivo kinetics of simultaneously injected 111In- and 51Cr-labelled human platelets.

The kinetics of simultaneously injected 111In- and 51Cr-labelled platelets have been assessed in 40 subjects, 13 of them thrombocytopenic. 4 platelet survival models were applied. The mean life-time (MLT) of 51Cr-platelets from non-thrombocytopenic individuals was found to be slightly, but significantly, longer than that of 111In-platelets by applying linear and exponential models for data fitting. The in vivo recovery (IVR) of 111In-platelets was significantly higher than that of 51Cr-platelets in this patient group when using all 4 models. In the group of thrombocytopenic patients no statistically significant differences in MLT or IVR were found between 111In- and 51Cr-platelets. However, for each of the 11 51Cr-labelled platelet suspensions with the shortest MLT, a longer MLT was observed in the corresponding 111In-platelets, a finding probably related to antibody-induced elution of 51Cr-activity. The same mechanism might be responsible for an increasing 111In-/51Cr-recovery ratio in the early post-injection period. The efficiency of platelet isolation from blood prior to labelling seemed to influence the IVR, inasmuch as the difference in IVR between 111In- and 51Cr-platelets was eliminated in the group where the yield of 111In-platelets surpassed that of the 51Cr-platelets by more than 15%.