Test Details: Immunoglobulin M (IgM) antibodies are produced as a bodys first response to a new infection or to a new foreign antigen, providing short-term protection. Their levels increase for short duration and later decline as IgG production begins. IgM also plays an important role in immune regulation and immunological tolerance. Demonstrating IgM antibodies in a patient's serum indicates recent infection, or in a neonate's serum indicates intrauterine infection e.g. congenital rubella syndrome.