Use

Serologic testing for measles-specific IgG is useful for assessing immunity from prior infection or vaccination, while detection of IgM antibody indicates recent or current infection. Results must be interpreted in context of timing relative to rash onset and may produce false positives or negatives. PCR testing of respiratory specimens may be preferred for confirming acute cases. Quest recommends collecting both serum for IgM/IgG and respiratory swabs for PCR in suspected measles, particularly early in disease course. Seroconversion or a ≥4-fold rise in IgM titer between acute and convalescent specimens supports diagnosis.