Microparticles are small membrane derived vesicles shed by activated or apoptotic cells typically less than 1 micron in size. These cell membrane fragments, present in the circulating blood, mimic the surface characteristics of the cell at the time of the microparticle formation; therefore, their individual characteristics are specific to different disease states. Their composition is primarily phospholipids and proteins and cellular origin dependent. They vary in size and quantity. Microparticles are derived from endothelial cells, platelets, leukocytes, erythrocytes, lymphocytes and vascular smooth muscle cells.

Microparticles are known to play an active role in the coagulation and inflammatory processes. Although microparticles are seen in normal healthy individuals, several investigators have noted elevated levels of microparticles in hypercoagulable states such as acute coronary syndrome, pre-eclampsia and stroke. The pathophysiology of cardiovascular disease is mirrored by elevated inflammatory response. Microparticles derived from platelets may trigger inflammation. Cytokines released by endothelial cells attract leukocytes to the endothelium initiated by microparticles.

Detection and accurate identification of the number, size and phenotype of microparticles can be the earliest warning signal of cellular damage or disease progression. This is critical in clinical diagnostic procedures and therapeutic monitoring.