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Test Code SLFAT Cryptococcus Antigen Titer, Lateral Flow Assay, Serum

Useful For

Monitoring Cryptococcus antigen titers in serum

 

Aiding in the diagnosis of cryptococcosis

 

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

Disease States

  • Cryptococcosis

Reporting Name

Cryptococcus Ag Titer, LFA, S

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial


Specimen Minimum Volume

0.3 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 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 

Reference values apply to all ages.

Interpretation

The presence of cryptococcal antigen in any body fluid (serum or cerebrospinal fluid) is indicative of cryptococcosis.

 

Disseminated infection is usually accompanied by a positive serum test.

 

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 resolution of infection.(3,4)

Cautions

Cryptococcus antigen titers acquired by the lateral flow assay (LFA) may be higher than titers achieved by other Cryptococcus antigen assays. Titers acquired by different assay methods are not interchangeable.

 

Cryptococcus antigen titers should be followed using the same assay.

 

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 samples 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

End-point titers between the IMMY Cryptococcus antigen lateral flow assay (LFA) and the Meridian latex agglutination test were compared for 10 samples positive for Cryptococcus antigen. While the overall qualitative correlation was good, these data indicate that the end-point titer achieved by the IMMY LFA was at least 2-fold higher than that achieved by the Meridian latex agglutination assay in 8 of 10 (80%) serum samples (Table).(5) Therefore, Cryptococcus antigen titers should be monitored by using the same method on serially collected samples; titers acquired by different methods are not interchangeable.

Table.  Reciprocal endpoint titer

Serum sample

Meridian latex agglutination

IMMY LFA

1

256

160

2

8

10

3

16

80

4

1024

2560

5

Negative*

10

6

8

20

7

2

10

8

4

10

9

64

160

10

8

20

  *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.

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. 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

4. 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

5. Binnicker MJ, Jespersen DJ, Bestrom JE, Rollins LO: A comparison of four assays for detection of cryptococcal antigen. Clin Vaccine Immunol. 2012 Dec;19(12):1988-1990

6. 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

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-cryptococcal antigen monoclonal antibodies and gold-conjugated control antibodies deposited on the test membrane. If cryptococcal antigen is present in the specimen, it binds to the gold-conjugated, anti-cryptococcal antigen antibodies. This complex wicks up the membrane and interacts with the test line, which has immobilized anti-cryptococcal 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

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.

CPT Code Information

87899

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SLFAT Cryptococcus Ag Titer, LFA, S 9818-6

 

Result ID Test Result Name Result LOINC Value
62077 Cryptococcus Ag Titer, LFA, S 9818-6

Method Name

Lateral Flow Assay (LFA)

Forms

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