Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1395 page)

   Inflammation and swelling of the parotid glands (parotitis) in mumps infection are usually sufficiently diagnostic to preclude serologic confirmation. However, inasmuch as one third of mumps infections are subclinical, viral isolation, and/or some other serologic procedure may be required.

   
Normal range:
Negative.

   Use

   Virus isolation is cumbersome and time consuming and is usually an impractical procedure for the typical clinical laboratory. Serodiagnosis of mumps infection has been accomplished by neutralization, hemagglutination inhibition (HI), indirect immunofluorescence, and complement fixation (CF). These methods lack specificity, which limits their usefulness in determining immune status. The HI test also requires pretreatment of test sera to remove nonspecific inhibitors of hemagglutination.

   Enzyme immunoassays (EIA, ELISA) are sensitive and specific, and their sensitivity equals that of the neutralization test and is greater than CF or HI. They are, therefore, reliable tests for the determination of immune status. Serum IgM antibody testing should be obtained no earlier than 3 days following initial onset of symptoms. The test typically remains positive for up to 4 weeks but may be negative in up to 50–60% of specimens from individuals with acute disease who were previously immunized. A negative IgM titer in vaccinated individuals, therefore, does not rule out mumps. Immunity to mumps is established by demonstrating IgG antibodies on ELISA.

   The test is used to assist in the diagnosis of acute-phase infection with mumps virus and to assist in identifying nonimmune individuals.

   Interpretation

   Positive IgM results, with or without positive IgG results, indicate a recent infection with mumps virus.

   Positive IgG results coupled with a negative IgM result indicate previous exposure to mumps virus and immunity to this viral infection.

   Negative IgG and IgM results indicate the absence of prior exposure to mumps and nonimmunity.

   Equivocal results should be followed up with a new serum specimen within 10–14 days.

   Limitations