Background: A new flow cytometric monocyte phagocytic assay (FMPA) was developed with 5-chloromethyl fluorescein diacetate (CMFDA)-labeled platelets for predicting the outcome of platelet transfusion.
Study design and methods: Twelve patients with a history of multiple platelet transfusions and 21 controls were enrolled in this study. Platelets labeled with CMFDA were incubated with patient serum and then incubated with monocytes. They were then analysed by flow cytometry. Monocytes that had phagocytized platelets (%) were detected as a CMFDA-positive platelet population with a CD14+ monocyte gate. The performance of FMPA was evaluated in 29 transfusions by 1- and 24-hour CCIs and platelet crossmatching.
Results: FMPA results were well correlated with 1-hour (r = -0.818, p = 0.001) and 24-hour (r = -0.782, p = 0.001) CCIs. In the group with high FMPA results (mean +/- SD, 79.1 +/- 7.3%), nine of 10 positive crossmatches revealed low CCIs, and six of seven negative crossmatches revealed high CCIs. The CCI predictability of crossmatching in the group with high FMPA results was high (88.2%). In the group with low FMPA results (mean +/- SD, 34.6 +/- 7.8%), all 12 transfusions revealed high CCIs even though in four transfusions there were positive results in both platelet antibody testing and platelet crossmatching.
Conclusion: FMPA is designed with near in vivo conditions to measure an immune response to transfused platelets, including phagocytosis. This is a useful method for predicting the outcome of platelet transfusion.