The Mumps IgM and IgG tests are performed using ELISA (Enzyme Linked Immunosorbent Assay) test kits manufactured by Euroimmun Diagnostics (Germany). The IgM and IgG ELISA tests measure human antibodies of the IgM and IgG classes against mumps virus in serum or plasma. Test results are reported qualitatively together with a clinical interpretation based on the status of both IgM and IgG.
After a primary infection, both IgM and IgG antibodies develop within 3-7days after onset of mumps specific symptoms. Both antibodies subsequently increase reaching a plateau 2-3 weeks later.
Antibody levels may be reported as Non-Reactive (no detectable antibody), Indeterminate (the level of antibody detected is considered borderline reactive or equivocal) or Reactive (antibody is detectable within the positive range of the assay).
Non-Reactive and Indeterminate levels of both IgM and IgG antibodies may be observed in the acute stage of infection rising to reactive levels in subsequent weeks.
In the absence of acute infection indeterminate levels of IgG may represent very low levels of antibody many years after initial infection or vaccination whereas indeterminate levels of IGM may be due to declining levels of IGM several months post infection or occasionally due to assay non-specificity.
If the acute blood sample shows low reactive, indeterminate or non reactive IgG result and/or IgM result, a convalescent sample should be collected. Recent infection is confirmed if a significant rise in antibody levels is observed between acute and convalescent sera.
For more information concerning the interpretation of diagnostic IgM and IgG serology refer to the document titled: LAB-SD-044, Diagnostic Interpretation of Viral Specific IgM and IgG Serology.