Chemiluminescent immunoassay (CLIA)

The absence of IgM at birth does not rule out congenital rubella since the frequency of IgM detection in cord blood decreases as the time between conception and fetal infection increases. Acquired rubella infection in infants is rare but must be considered if the blood is positive for IgM but was not obtained during the immediate postnatal period. Rubella-specific IgM may persist for months after an acute infection and, possibly, after vaccination as well. False-positive rubella IgM responses have been reported following mononucleosis, parvovirus B19 infections, and possibly other herpes-type viral infections. False-positive rubella IgM responses have also been reported in pregnant women. These reactions are usually accompanied by false-positive reactions to other viruses (eg, CMV and measles).

Hemolysis; lipemia; gross bacterial contamination