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Cryptococcal Antigen

Cryptococcus neoformans is acquired by inhalation and causes pneumonia. It may disseminate from the lungs and invade the CNS causing meningitis. Other viscera, bone, and skin may also be involved. Cryptococcosis can occur as a primary disease or secondary to immunosuppression. Previously, cryptococcal meningitis was diagnosed by staining CSF with India Ink. A more sensitive cryptococcal antigen test has replaced the India ink test and can detect fungus in both serum and CSF.

The cryptococcal antigen test has both diagnostic and prognostic value. Positive specimens are titrated and the highest titers are reported. CSF titers of 1:8 or higher are considered strong evidence of active infection. The antigen titer is proportional to the extent of infection, with increasing titers indicating progressive infection. Response to chemotherapy can be monitored with serial titers. Decreasing titers suggest a favorable response, while unchanging or increasing titers suggest unsuccessful treatment.

Specimen requirement is one SST tube of blood or 1 mL of spinal fluid.

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