Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1392 page)

   
Common pitfall:
Nonhuman pathogens, like earthworms, may be submitted for examination.

MEASLES SEROLOGY SCREEN (MEASLES [RUBEOLA] IgG AND IgM)
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   Definition

   Measles is a highly contagious, acute, exanthematous disease caused by the measles (rubeola) virus. It is generally self-limiting and without serious consequences, although complications such as bronchopneumonia and otitis media do occur. The most serious consequence is encephalomyelitis (about 1 in 10,000 cases). Natural infection with measles virus confers permanent immunity. Measles infection poses a serious threat to immunosuppressed or immunocompromised patients. For these reasons, the laboratory diagnosis of measles has become increasingly important, notwithstanding the reduction in the incidence due to the introduction of vaccines.

   The usual means of laboratory diagnosis of acute measles is serologic, by the demonstration of either a fourfold or greater rise in virus-specific IgG antibody in acute and convalescent serum pairs, or by the detection of virusspecific IgM antibody in a single, early serum specimen.

   
Normal range:
Negative.

   Use

   To assist in the diagnosis of acute-phase infection with rubeola (measles) virus and assist in identifying nonimmune individuals.

   Interpretation

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

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

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

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

   False-positive measles IgM results can occur due to cross reactivity with rheumatoid factor, parvovirus, rubella and roseola antibodies.