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Cryptococcus Antigen-Provincial

Discipline

Microbiology

Overview

Description

Cryptococcosis is an invasive fungal infection caused by the Cryptococcus species complex (Cryptococcus neoformans and Cryptococcus gattii). Infection often occurs through inhalation of soil contaminated with the encapsulated yeast cells. Detection of cryptococcal antigen (CrAg) in human serum and CSF is diagnostic with very high sensitivity and specificity (99% or higher).

Ordering Recommendations

  • Individuals with impaired cell-mediated immunity are at greatest risk of infection. Cryptococcosis is one of the most common opportunistic infections in AIDS patients. Patients with lymphoma, sarcoidosis, or on long-term corticosteroid therapy are also at increased risk. 

  • Disease can be pulmonary only or can disseminate to the meninges, skin, viscera, bones and other body sites. 

  • Progressive disseminated cryptococcosis rarely occurs in non-immunocompromised patients, with higher frequency in men over 40 years of age. 

  • The predictive value of a positive or negative serologic result depends on the pretest likelihood of cryptococcal disease being present. Testing should only be performed when clinical evidence suggests the diagnosis of cryptococcal disease.

Alias

  • CrAg, CrAg lateral flow, CrAg latex agglutination

Specimen Information

Specimen types accepted

  • CSF, serum 

Specimen collection container

  • Blood (Serum): Serum separator tube (gold top)

  • Blood (clotted): Red top vacutainer tube

  • CSF: Sterile container 

Collection procedure

  • Centrifuge SST prior to transport

  • Serum samples must NOT contain any anticoagulant

  • Hemolysed, icteric or lipemic samples are not recommended for testing

Required volume

  • 0.5 mL CSF (needs to be sent for fungal culture 1ml is preferred)

  • 5.0 mL blood or 1.0 mL serum

Transport and stability

  • Store and ship at 2-8 °C

Testing Information

Relevant clinical history

Patient History

  • Hook effect: Although rare, extremely high concentrations (> 0.150 mg/mL) of cryptococcal antigen can result in weak test lines and, in extreme instances, yield negative test results. If high clinical suspicion persists following negative test results, please notify the laboratory to rule out prozone effect.

  • Accompanying fungal culture and smear should be ordered for all CSF specimens submitted for Cryptococcal antigen testing.  

Performance

Methodology

  • Cryptococcus capsular polysaccharides are detected via a lateral flow immunochromatography both qualitatively (positive/negative) and quantitatively (titer). 

Days/times performed

  • All specimens will be tested at the nearest microbiology laboratory

Maximum laboratory time

  • Turnaround time of 2-4 hours from receipt in lab for CSF

  • (4 weeks for final on fungal culture)

  • 24h Turnaround time for serum

Specimen retention time

RGH/Pasqua

  • Serum specimens are retained for 7 days after initial processing

  • CSF kept for 1 month
Saskatoon

  • Serum retained for 3 days after initial processing. 

  • CSF retained for 7 days after initial processing. 

 

 

 

 

 

 

 

 

Last Updated: November 17, 2025