Support the diagnosis of Mumps infection. The presence of IgG antibody generally indicates past exposure and immunity. The presence of IgM antibody or a fourfold or greater rise in IgG antibodies in paired sera indicates recent infection. Single IgG levels are not useful for supporting the diagnosis of acute infection. Elevated responses in neonates should be followed up with studies to rule out the presence of maternal antibodies, either by obtaining a convalescent specimen or by the demonstration of the absence of an IgM response.