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Test Code SLFA Cryptococcus Antigen Screen with Titer, Serum

Useful For

Aiding in the diagnosis of cryptococcosis

 

This test should not be used as a test of cure or to guide treatment decisions.

 

This test should not be used as a screening procedure for the general populations.

Disease States

  • Cryptococcosis

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
SLFAT Cryptococcus Ag Titer, LFA, S Yes No

Testing Algorithm

If result is positive, Cryptococcus titer will be performed at an additional charge.

Reporting Name

Cryptococcus Ag Screen w/Titer, S

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days
  Frozen  14 days

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject

Clinical Information

Cryptococcosis is an invasive fungal infection caused by Cryptococcus neoformans or Cryptococcus gattii. C neoformans has been isolated from several sites in nature, particularly weathered pigeon droppings. C gattii was previously only associated with tropical and subtropical regions. More recently, however, this organism has been found to be endemic in British Columbia and the Pacific Northwestern United States and is associated with several different tree 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 individuals.(1,2)

 

In addition to the lungs, cryptococcal infections frequently involve the central nervous system (CNS), particularly in patients infected with HIV. Mortality among patients with CNS cryptococcosis may approach 25% despite antibiotic therapy. Untreated CNS cryptococcosis is invariably fatal. Disseminated disease may affect any organ system and usually occurs in immunosuppressed individuals.

Reference Values

Negative

Interpretation

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 to generate a titer value.

 

Disseminated infection is usually accompanied by a positive serum test.

 

Higher Cryptococcus antigen titers appear to correlate with more severe infections. Declining titers may indicate regression of infection. However, monitoring titers to cryptococcal antigen should not be used as a test of cure or to guide treatment decisions. Low-level titers may persist for extended periods of time following appropriate therapy and the resolution of infection.(3)

Cautions

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.

 

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.

 

Although rare, extremely high concentrations of cryptococcal antigen can result in weak test lines and in extreme instances, yield negative test results.

 

This assay has not been evaluated for cross-reactivity in patients with trichosporonosis.

Supportive Data

There were 634 serum specimens (632 prospective and 2 archived) tested in a blinded fashion by the IMMY Cryptococcus antigen lateral flow assay (LFA), the Meridian latex agglutination (Meridian Bioscience Inc) assay, and the Meridian Cryptococcus antigen enzyme immunoassay (EIA) within a 24-hour period. Specimens with discordant results after initial testing were repeated by both assays during the same freeze/thaw cycle. The results are summarized in Table 1 and Table 2 below:

 

Table 1: Comparison of the IMMY LFA to the Meridian latex agglutination assay

 

Meridian latex agglutination

IMMY LFA

 

Positive

Negative

Total

Positive

9

1*

10

Negative

0

624

624

 Total

9

625

634

*This sample showed 1+ reactivity by the Meridian latex agglutination assay upon screening but was interpreted as negative according to the package insert requirement for 2+ reactivity.

Sensitivity: 100% (9/9); 95% CI: 65.5%-100%

Specificity: 99.8% (624/625); 95% CI: 99.0%-99.9%

Overall Percent Agreement: 99.8% (633/634); 95% CI: 99.0%-99.9%

 

Table 2: Comparison of the IMMY LFA to the Meridian Cryptococcus antigen EIA

Meridian EIA

IMMY LFA

 

Positive

Negative

Total

Positive

5

5*

10

Negative

0

624

624

 Total

5

629

634

*These 5 samples were positive by the Meridian latex agglutination assay

Sensitivity: 100% (5/5); CI: 51.7%-100%

Specificity: 99.2% (624/629); CI: 98.1%-99.7%

Overall Percent Agreement: 99.2% (629/634); CI: 98.1%-99.7%

Clinical Reference

1. Speed B, Dunt D: Clinical and host differences between infections with the two varieties of Cryptococcus neoformans. Clin Infect Dis. 1995;21(1):28-34

2. Chen S, Sorrell T, Nimmo G, et al: Epidemiology and host- and variety-dependent characteristics of infection due to Cryptococcus neoformans in Australia and New Zealand. Australasian Cryptococcal Study Group. Clin Infect Dis. 2000 Aug;31(2):499-505. doi: 10.1086/313992

3. Perfect JR, Dismukes WE, Dromer F, et al: Clinical practice guidelines for the management of cryptococcal disease: 2010 update by the Infectious Diseases Society of America. Clin Infect Dis. 2010 Feb 1;50(3):291-322

4. Warren NG, Hazen KC: Candida, Cryptococcus, and other yeasts of medical importance. In: Murray PR, ed. Manual of Clinical Microbiology. 7th ed. ASM Press; 1999:1184-1199

5. Lu H, Zhou Y, Yin Y, Pan X, Weng X : Cryptococcal antigen test revisited: significance for cryptococcal meningitis therapy monitoring in a tertiary Chinese hospital. J Clin Microbiol. 2005 June;43(6):2989-2990

6. Perfect JR: Cryptococcosis (Cryptococcus neoformans and Cryptococcus gattii). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020:3146-3161

Method Description

The Cryptococcus antigen (CrAg) lateral flow assay is a sandwich immunochromatographic assay. Specimens and diluent are added to a test tube and the lateral flow device is added. The test uses specimen wicking to capture gold-conjugated, anti-Cryptococcus antigen monoclonal antibodies and gold-conjugated control antibodies deposited on the test membrane. If Cryptococcus antigen is present in the specimen, it binds to the gold-conjugated, anti-Cryptococcus antigen antibodies. This complex wicks up the membrane and interacts with the test line, which has immobilized anti-Cryptococcus antigen monoclonal antibodies. The antigen-antibody complex forms a sandwich at the test line causing a visible line to form. A valid test shows a visible line at the control line. Positive test results create 2 lines (control and specimen) while negative results form only the control line.(Package insert: CrAg Lateral Flow Assay. IMMY; Rev 06/27/2019)

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 to 2 days

Specimen Retention Time

14 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

87899

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SLFA Cryptococcus Ag Screen w/Titer, S 29903-2

 

Result ID Test Result Name Result LOINC Value
62075 Cryptococcus Ag Screen w/Titer, S 29903-2

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

Method Name

Lateral Flow Assay (LFA)

Forms

If not ordering electronically, complete, print, and send Infectious Disease Serology Test Request (T916) with the specimen.