Cryptococcosis laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Serge Korjian M.D.; Yazan Daaboul, M.D.
Overview
Laboratory Findings
Cryptococcal disease can be diagnosed through culture, CSF microscopy, or by cryptococcal antigen (CrAg) detection. In patients with HIV-related cryptococcal meningitis, 55% of blood cultures and 95% of CSF cultures are positive and visible colonies can be detected within 7 days. The opening pressure in the CSF may be elevated, with pressures ≥25 cm H2O occurring in 60% to 80% of patients.
Culture
- The gold standard for diagnosing cryptococcal infection; culture is traditionally identify Cryptococcus from human body samples.
- Blood cultures may be positive in heavy infections.
Microscopy
- India Ink can be performed on CSF to quickly visualize Cryptococcus cells under a microscope; however, it can have limited sensitivity.
- Many laboratories in the United States no longer perform this test.
- Histopathology for detection of narrow-based budding yeasts in tissue can also be used.
Antigen detection
- Antigen detection can be used on CSF or serum for detection of early, asymptomatic cryptococcal infection in HIV-infected patients.
- It has a higher sensitivity than microscopy or culture.
- CSF CrAg is usually positive in patients with cryptococcal meningoencephalitis. Serum CrAg is usually positive in both meningeal and non-meningeal infection and may be present weeks to months before symptom onset.
- A positive serum CrAg should prompt a lumbar puncture to rule out meningeal disease.
- Techniques used include:
- Latex agglutination (LA)
- Enzyme immunoassay (EIA)
- Lateral flow assay (LFA)