XDx, also known as Expression Diagnostics, is a molecular diagnostics company that specializes in the discovery, development and commercialization of noninvasive gene expression testing. The company has expertise in the areas of transplant medicine and autoimmunity. Established in 2000, XDx has developed a proprietary method of utilizing gene expression in blood that provides a new tool for physicians to manage the care of heart transplant patients. It offers a proprietary product called AlloMap that is used in molecular expression testing. XDx maintains its headquarters in Brisbane, Calif.