Yellow fever laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Multiple laboratory abnormalities can be observed in patients with yellow fever, including leukopenia or leukocytosis, bleeding dyscrasias, thromobcytopenia, increased billirubin and hepatic enzymes.
Laboratory Findings
Routine Tests
- Laboratory findings can vary depending on the severity and stage of illness. [1]
- In the first week of the illness, leukopenia might occur; however, leukocytosis also can occur during the second week of the disease.
- Bleeding dyscrasias also can occur, together with elevated prothrombin and partial thromboplastin times, decreased platelet count, and presence of fibrin-split products.
- Hyperbilirubinemia might be present as early as the third day but usually peaks toward the end of the first week of illness.
- Elevations of serum transaminase levels occur in severe hepatorenal disease and might remain elevated for up to 2 months after onset.
- Laboratory diagnosis generally is accomplished by testing serum to detect virus-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies by serologic assays.
Serology
- Initial serological testing will be performed using IgM-capture ELISA, MIA (Microsphere-based Immunoassay) and IgG ELISA.
- It is important to obtain a yellow fever vaccination history, as IgM antibodies to yellow fever vaccine virus can persist for several years following vaccination.
- Serologic cross-reactions occur with other flaviviruses (e.g., West Nile or dengue viruses), so positive results should be confirmed with a more specific test (e.g., plaque-reduction neutralization test).
Molecular Tests
- During the first 3-4 days of infection, yellow fever virus or yellow fever virus RNA often can be detected in the serum by virus isolation or nucleic acid amplification testing.
- However, by the time overt symptoms are recognized, the virus or viral RNA usually is undetectable. Therefore, negative virus isolation and RT-PCR results cannot rule-out the diagnosis of yellow fever.
- Immunohistochemical staining of formalin-fixed material can detect yellow fever virus antigen in histopathologic specimens.