A single elevated serum sample cannot be considered diagnostic of SSPE (sub-sclerosing pan ecephalitis). While cases of SSPE may have responses of 10 - 100X those generally seen, the best indicator is the detection of elevated levels of IgG specific for rubeola antigens in CSF as compared to those found in serum, suggesting local IgG production in CSF. In persons with normal immune systems, postinfectious encephalitis has no accompanying enhanced antibody response. Increasing titers of serum antibodies to rubeola virus, as well as other viruses (rubella), have been associated with active chronic hepatitis, systemic lupus erythematosus and infectious mononucleosis. The performance characteristics of this test have not been established for CSF, neonates, infants or cord blood. This is a qualitative test; quantitation for comparison of acute and convalescent sera has not been validated by the manufacturer of the current test system. Result values from different methodologies or from different institutions cannot be compared. Timing of specimen collection for paired sera is critical. In some patients, antibody may rise to significant levels and fall again to lower or undetectable levels within a month. Other patients may not develop significant antibody levels.