Cryptococcal Antigen Latex Agglutination – Direct Blood and CSF

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides information on cryptococcal antigen Latex agglutination testing at Public Health Ontario’s (PHO) laboratory. The causative agent(s) of cryptococcosis is Cryptococcus neoformans. This page is for information specific to Antigen Latex Agglutination testing. Antibody testing is not available at PHO’s laboratory.

The Cryptococcal Antigen Latex Agglutination System (CALAS) is a qualitative and semi-quantitative test system for the detection of capsular polysaccharide antigens of Cryptococcus neoformans in serum and cerebrospinal fluid (CSF).

*Uncontrolled print copy. Valid only on day of print: 01 May 2024.

Testing Indications

Cryptococcosis is an infection acquired by inhalation of soil contaminated with the encapsulated yeast Cryptococcus neoformans, which may cause a self-limited pulmonary infection or disseminate, especially to the meninges, but sometimes to the skin, bones, viscera, or other sites¹.

Distribution is worldwide. Cryptococcosis is a defining opportunistic infection of AIDS, although patients with Hodgkin’s or other lymphomas, sarcoidosis or those receiving long-term corticosteroid therapy are also at an increased risk. Progressive disseminated cryptococcosis also sometimes affects those who are not obviously immunocompromised, more frequently men > 40 yr.¹

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Cryptococcal Antigen	General Test Requisition	Whole blood Serum	5.0 ml blood or 1.0 ml serum	Blood, clotted - Must contain no anti-coagulant (red top vacutainer) or serum separator tubes (SST)
Cryptococcal Antigen	General Test Requisition	CSF	0.5 mL	Sterile container

Submission and Collection Notes

Complete all fields of PHO’s General Test Requisition Form. Include the patient’s full name, date of birth, and Health Card Number (must match the specimen label), physician name and address, and mandatory clinical information:

Test(s) requests and indications for testing
Clinical information including symptom onset date

For clinical specimens, label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

Limitations

Serum samples must not contain anti-coagulant.
Haemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing

Storage and Transport

Centrifuge if using SST prior to transport. Place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to PHO’s laboratory on ice packs as soon as possible. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Cryptococcal Ag direct CSF/blood testing is performed 3 times per week at PHO’s laboratory

Testing is not available on weekends.

Turnaround time is up to 3 business days from receipt at the PHO’s laboratory.

Stat and Critical Specimens Testing

For Priority/STAT requests:

Notify PHO’s Laboratory Customer Service Centre of the incoming priority/STAT request at 416-235-6556/1-877-604-4567 prior to submitting a specimen for STAT testing.
Ship priority/STAT specimens separately from routine specimens in accordance with the Transportation of Dangerous Goods Regulations.
Clearly mark packaging with “PRIORITY/STAT WRA-Immuno Laboratory” for easier identification and retrieval upon arrival at the PHO laboratory.
Ship priority/STAT specimens directly to PHO’s laboratory Toronto site at 661 University Ave., Toronto, Ontario. For delivery instructions please see Directions to 661 University Shipping Dock for Clinical Samples.
Failure to follow the submission instructions above may result in testing delays.

Note: For expedited testing of critical specimens, please call PHO’s Laboratory Customer Service Centre at 416-235-6556/1-877-604-4567, to ensure they are prioritized and/or tested on next available run.

Test Methods

Cryptococcal Antigen Latex Agglutination System (CALAS®) is a qualitative and semi-quantitative test system for the detection of capsular polysaccharide antigens of Cryptococcus neoformans in serum and CSF.

Both blood and spinal fluid are tested for cryptococcal antigen – not antibody. Cryptococcal antigen can be detected in the CSF of patients with cryptococcal meningitis, especially in patients with HIV/AIDS. Patients on treatment with rising antigen titers in CSF or serum should be assessed for persistence or recurrence of infection.

Assay Performance¹:

According to the manufacturer, the Calas Agglutination kit using a pronase step was shown to be 100% sensitive and 100% specific when compare to a Monoclonal Based EIA procedure. The Pronase step was shown to reduce 1) rheumatoid factor (RF) reactions, 2) Prozone effects at high antigen concentrations, and 3) false negative due to apparent masking of antigen following certain antibiotic therapies¹.

Assay Limitations¹:

A negative CALAS test does not preclude diagnosis of cryptococcosis, particularly if only a single specimen has been tested and the patient shows symptoms consistent with cryptococcosis¹
Cross reactions/false positives can occur (eg. a cross reaction has been reported in a serum specimen from a patient with disseminated Trichosporon infection) ¹.
Although the presence of non-specific interference can invalidate the CALAS test results, this does not exclude the possibility of cryptococcal infection since cryptococcosis can occur concomitantly with other conditions¹.

Algorithm

CSF is tested undiluted:
If there is no Agglutination, it will be reported as Not Detected: Undiluted.

If there is Agglutination, a twofold serial dilution titration will be performed to determine the end point.

Blood tested at a 1:2 dilution with pronase:
(Pre-treatment with pronase reduces nonspecific interference and enhances the detection of capsular polysaccharide antigens).

If there is no Agglutination, it will be reported as Not Detected: <1:2

If there is Agglutination, a twofold serial dilution titration will be performed to determine the end point.

Interpretation

The following table provides possible test results with associated interpretations:

Result	Interpretation	Comments
Blood titre : <1:2 CSF titre : Undiluted	Cryptococcus neoformans Ag by Latex Agglutination- Not Detected
Blood titre : ≥1:2	Cryptococcus neoformans Ag by Latex Agglutination- Detected
CSF titre : ≥1:1*	Cryptococcus neoformans Ag by Latex Agglutination- Detected
Unable to determine	Cryptococcus neoformans Ag by Latex Agglutination- Non- Specific	Please resubmit specimen if clinically indicated.

*While CSF titers of 1:4 or less are presumptive evidence of central nervous system infection by C. neoformans, additional follow-up and culture are strongly recommended. CSF titers of 1:8 or greater from patients with meningitis strongly suggest infection by C. neoformans. However, diagnosis should be confirmed by identification of the organism from culture or by microscopic examination of the specimen1.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

References

Kit Insert: Cryptococcal Antigen Latex Agglutination System (CALAS®) Meridian Diagnostics, Inc. Cat # 140100 SN 10100 Rev 7/96