Tracking and characterisation of transfused platelets by two colour, whole blood flow cytometry

We describe a flow cytometric technique to study transfused platelets in patients. By selecting donor/recipient pairs discrepant for HLA-A2, transfused platelets were identified using anti-HLA-A2 with a detection limit of <5%, and accuracy within 4.3% of predicted (r(2) > 0.96, P < 0.0001). In two of three episodes, transfused platelets were present in greater numbers than predicted from increment counts. Platelets with bound fibrinogen fell from 20.9 +/- 23.6% of donor platelets pretransfusion to 1.7 +/- 0.3% 1 h post-transfusion, whereas P-selectin-positive platelets fell gradually, from 24.1 +/- 6.7 to 7.3 +/- 3.3% at 6 h. This method avoids radio or chemical labelling, and could be used to assess novel platelet preparations post-transfusion.