Platelet/leukocyte interaction assay and reagent therefor

A platelet/leukocyte interaction assay method, comprising:

• contacting a whole blood or blood-derived sample containing platelets and leukocytes with a platelet/leukocyte interaction assay reagent in the presence of an oscillating or rotating magnetic field, said platelet/leukocyte interaction assay reagent comprising a leukocyte marker compound and a mixture of magnetic and non-magnetic particles, wherein said magnetic particles have bound to an outer surface thereof an amount of a first ligand having an affinity for direct interaction with blood platelets and wherein said non-magnetic particles have bound to an outer surface thereof an amount of a second ligand having an affinity for direct interaction with blood platelets, wherein said first ligand and said second ligand can be the same or different;
• and
• monitoring movement of the magnetic particles in response to the oscillating or rotating magnetic field, to determine the presence or absence of platelet/leukocyte interaction function, a level of platelet/leukocyte interaction, or both, in the whole blood or blood-derived sample containing platelets and leukocytes as determined by comparing a level of leukocyte marker compound in an aggregate formed of said magnetic and non-magnetic particles to a level of leukocyte marker compound outside of said aggregate.