Cryptococcus Antigen Test

Cryptococcosis is an invasive fungal infection caused by Cryptococcus neoformans or Cryptococcus gattii. C. neoformans has been isolated from several sites in nature, particularly feathered pigeon droppings. C.gatti was previously associated with tropical and subtropical regions; however, more recently this organism has also been found to be endemic in British Columbia and among the Pacific Northwest United States, and is associated with several different trees species. Infection is usually acquired via the pulmonary route. Patients are often unaware of any exposure history. Approximately half of the patients with symptomatic disease have a predisposing immunosuppressive condition such as AIDS, steroid therapy, lymphoma, or sarcoidosis. Symptoms may include fever, headache, dizziness, ataxia, somnolence, and cough. While the majority of C. neoformans infections occur in immunocompromised patient populations, C.gattii is has a higher predilection for infection of healthy hosts.

Testing should not be performed as a screening procedure for the general populations and should only be performed when clinical evidence suggests the diagnosis of cryptococcal disease. Testing hemolyzed serum specimens may lead to false-negative results due to the high background color on the lateral flow assay strip.

An aid in the diagnosis of cryptococcosis. The presence of cryptococcal antigen in any body fluid (serum or cerebrospinal fluid) is indicative of cryptococcosis. Specimens that are positive by the lateral flow assay screen are automatically repeated with the same method utilizing dilutions in order to generate a titre value. A negative result does not preclude diagnosis of cryptococcosis, particularly if only a single specimen has been tested and the patient shows symptoms consistent with cryptococcosis. A positive result is indicative of cryptococcosis, however all test results should be reviewed in light of other clinical findings.

The presence of cryptococcal antigen in any body fluid (serum or cerebrospinal fluid) is indicative of cryptococcosis. Specimens that are positive by the lateral flow assay screen are automatically repeated with the same method utilizing dilutions in order to generate a titre value. Disseminated infection is usually accompanied by a positive serum test. Higher Cryptococcus antigen titres appear to correlate with more severe infections. Declining titres may indicate regression of infection. However, monitoring titres to cryptococcal antigen should not be used as a test of cure or to guide treatment decisions, as low level titres may persist for extended periods of time following appropriate therapy and the resolution of infection.