The diagnosis of erythema infectiosum usually is based on clinical presentation alone, and a workup for patients with the classic presentation is not necessary. For patients with other signs or symptoms associated with human PV-B19 or for exposure in a woman who is pregnant, confirmation of infection may be helpful and can be accomplished with the following specialized tests:
IgM assays: enzyme-linked immunosorbent assay, radioimmunoassay
Dot blot hybridization
Polymerase chain reaction assay
Loop-mediated isothermal amplification
Consider obtaining a complete blood cell count and serologic testing in the presence of coexisting hemolytic disease, pregnancy, or arthropathy. Human PV-B19 does not grow in standard blood or tissue culture systems.
Skin biopsy does not aid in diagnosis, but it may reveal nonspecific changes, including mild basilar vacuolation, dyskeratotic cells, and a sparse perivascular infiltrate. Antibody testing is usually available only through commercial reference laboratories or state health and research laboratories. These tests are unreliable for diagnosing infection in immunosuppressed patients.
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Cite this: William James. Fast Five Quiz: How Much Do You Know About These Common Rashes? - Medscape - Nov 16, 2016.