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

Cryptococcal disease can be diagnosed through culture, CSF microscopy, or by cryptococcal antigen (CrAg) detection.

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)