The Measles IgG and IgM tests are performed using ELISA (Enzyme Linked Immunosorbent Assay) test kits manufactured by Euroimmun (Germany). The IGG and IGM ELISA tests are both quantitative (IGG) and semi-quantitative (IGM) measuring human antibodies of the IgG and IgM classes against measles virus in serum or plasma. Test results are reported qualitatively together with a clinical interpretation based on the status of both IgG and IgM.
After a primary infection, both IgG and IgM antibodies develop within 3-7days after rash onset. Both antibodies then 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 IgG and IgM 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 possibly due to assay non-specificity.
If the acute blood sample shows low reactive, indeterminate or non reactive IgG and/or IgM results then 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 on the interpretation of serological results refer to the document titled: LAB-SD-044, Diagnostic Interpretation of Viral Specific IgM and IgG Serology.