Whole blood analysis of leukocyte-platelet aggregates.

In inflammatory and thrombotic syndromes, platelets aggregate with circulating leukocytes, especially monocytes and neutrophils. The platelet binding is initiated primarily through platelet surface expression of P-selectin (CD62P) following activation-dependent degranulation. The levels of P-selectin involved can be low enough to make direct measurement difficult, but detection of leukocyte-platelet aggregates is relatively simply by whole-blood flow cytometry. Light scatter and at least one leukocyte-specific antibody are used to gate the desired population, and the presence of associated platelets is detected by immunostaining for abundant platelet-specific markers.