0.90 IV or less
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Negative: No significant level of detectable Parvovirus B19 IgM antibody.
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0.91-1.09 IV
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Equivocal: Repeat testing in 7-21 days may be helpful
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1.10 IV or greater
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Positive: IgM antibody to Parvovirus B19 detected which may indicate a current recent infection.
However, low levels of IgM antibody may occasionally persist for more than 12 months post-infection.
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The best evidence for infection is a significant change on two appropriately timed specimens, where both tests are done in the same laboratory at the same time.
Appearance of an IgM antibody response normally occurs 7-14 days after the onset of diseases. Testing immediately post-exposure is of no value without a later convalescent specimen.
A residual IgM response may be distinguished from early IgM response to infection by testing sera from patients 3-4 weeks later for changing levels of specific IgM antibodies.
Immunocompromised patients may have a delayed or absent antibody response. Therefore, antibody levels may not be the optimal way to diagnose parvovirus infection in these patients. The best method in these situations is detection of parvovirus DNA in serum.