Our laboratory has examined in vivo platelet activation in multiple settings
and we find that it is a reliable test using flow cytometry. We fix the
platelets in paraformaldehyde (I know that some investigators do not fix and
must label the platelets stat). We then examine for CD62P or CD63 (they tend
to go together in our opinion so we usually just examine CD62P). One can
then quantitate the % of circulating activated platelets and the relative
amounts of CD62P expressed by the activated platelets.
We also examine the % of monocytes and neutrophils with bound platelets,
since CD62P is a ligand for activated platelet binding to phagocytes. We
find that this latter assay by flow may be more sensitive for platelet
activation when the physiologic agonist is relatively weak, i.e. increased
epinephrine in septic states.
-Harv Rinder