IgG antibodies to Histoplasma antigen appear to be associated with active infection, especially in cats with moderate to high positive (20 EU or greater) results. Antibodies may also be detected in a small percentage of healthy cats from the endemic area as a result of sub-clinical infection within the last 2 years. IgG may be detected in histoplasmosis cases with falsely-negative antigen results (especially with localized disease or chronic infection) and combined antibody and antigen testing increases the overall sensitivity. Intermediate results (8-9.9 EU) typically reflect either rising or falling IgG, and retesting the patient in several weeks may be beneficial.
Semi-Quantitative Indirect Enzyme Immunoassay (EIA)
~1/3 of patients with Blastomycosis or Coccidioidomycosis will exhibit cross reactivity.
Cross-reactivity/False Positives: Low: Histoplasma, Blastomyces, and Coccidioides (true positives are considerably higher than cross-reactive results)
The reference range and other method performance specifications have not been established for this test in CSF. The test results should be integrated into the clinical context for interpretation.
Testing is performed on Wednesdays and Fridays.
Serum or CSF: Next Day
Negative: <8.0 EU
Intermediate: 8.0 EU-9.9 EU
Positive:10.0 EU-80.0 EU
Positive Above the Limit of Quantification: >80.0 EU
Specimen: Serum, CSF*, Plasma*
*Uncommon specimen includes incomplete validation. A ’rare specimen’ note will appear on the final report.
Serum: Collect serum specimens in serum separator tube. Allow blood to clot for 30 minutes, then centrifuge. Send serum in serum separator tube or transfer tube
CSF, Plasma: Sterile transport tube
Anticoagulant: Heparin, EDTA, NaCit
Volume: 0.25 mL
Stability: Room temperature = 28 days, Refrigerated = 6 months, Frozen = indefinite
Ship overnight or 2nd day – ambient or with cold pack