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Microparticles (MPs) are small fragments of membrane-bound cytoplasm that are shed from the surface of an activated or apoptotic cell. Recently, their function as vectors of transcellular exchange of biologic information, in addition to better described forms of intercellular communication such as growth factors, cytokines, and chemokines, has become well recognized. Circulating levels of MPs are thought to reflect a balance between cell stimulation, proliferation, and death. The production of MPs is thought to predominately occur by vesiculation or blebbing of the cell membrane. The mechanisms governing the remodeling of the plasma membrane are complex, involving cytoskeletal changes and a shift from normal phospholipid asymmetry. Increased intracellular calcium subsequent to cell activation leads to intracellular increases in several proteins including gelsolin and calpain, as well as the activity of enzymes such as translocase, floppase, and scramblase, which play important roles in the homeostasis of the cell membrane. The membrane vesiculation and phospholipids asymmetry leading to the production of MPs occurs by the complex interplay of the proteins involved. There are several clinical conditions associated with elevated MPs, and most are also associated with an increased risk of thrombosis. Apart from cardiovascular disease and venous thromboembolism, MPs are also elevated in solid tumors with metastatic disease. The measurement of MPs is being regarded as a potential biomarker, given the range of conditions in which they are elevated and the association with prothrombotic states. The utility of measuring MPs as a diagnostic and prognostic marker is currently a subject of intense investigation. The further development of the various methods for the detection and measurement of MPs and prospective clinical trials establishing the utility of such tests will be critical prior to the routine measurement of MPs in the diagnostic laboratory. [ABSTRACT FROM AUTHOR]

Microparticles are small, membrane-bound vesicles that are generated from cells of different origin. It now appears that all circulating blood cells as well as endothelial cells release membranous fragments ~1 ?m in size or smaller bearing at least some characteristics of the parent cell. Elevated levels of microparticles have been described in cardiovascular states, thrombotic conditions, and cancer. Various methods of detection for microparticles include flow cytometry, enzyme-linked immunoassays, and functional assays. Flow cytometry has several advantages including its ability to quantitate and identify microparticles of different cellular origin. However, the standardization of preanalytical and analytical variables for enumeration of microparticles remains a significant challenge. Newer approaches are being investigated, and an international collaboration is working on standardization of detection as well as quantitation of microparticles by flow cytometry. Although it has evolved as an important vascular biology research tool, microparticle detection needs further evaluation and refinement before it becomes truly useful as a clinical tool. [ABSTRACT FROM AUTHOR]