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Test ID: SCOC Coccidioides Antibody, Complement Fixation and Immunodiffusion, Serum

Reporting Name

Coccidioides Ab, CompF/ImmDiff, S

Useful For

Diagnosis of coccidioidomycosis using serum specimens

Clinical Information

Coccidioidomycosis (valley fever, San Joaquin Valley fever) is a fungal infection found in the Southwestern US, Central America, and South America. It is acquired by inhalation of arthroconidia of Coccidioides immitis/posadasii. Usually, it is a mild, self-limiting pulmonary infection. Less commonly, chronic pneumonia may occur, progressing to fibronodular, cavitary disease. A rash often develops within a day or 2, followed by erythema nodosum or multiforme and accompanying arthralgias. About 2 weeks after exposure, symptomatic patients develop fever, cough, malaise, and anorexia; chest pain is often severe. Coccidioidomycosis may disseminate beyond the lungs to involve multiple organs, including the meninges.


IgG antibody is detected by the complement-fixation tests. Precipitating antibodies (IgM and IgG) are detected by immunodiffusion. They are rarely found in cerebrospinal fluid; however, their presence is associated with meningitis. Chronic coccidioidal pulmonary cavities are often accompanied by IgG and IgM precipitating antibodies.


Serologic testing for coccidioidomycosis should be considered when patients exhibit symptoms of pulmonary or meningeal infection and have lived or traveled in areas where C immitis/posadasii is endemic. Any history of exposure to the organism or travel cannot be overemphasized when a diagnosis of coccidioidomycosis is being considered.


Complement Fixation:

Titer results of 1:2 or higher may suggest active disease; however, titers may persist for months after infection has resolved. Increasing complement fixation (CF) titer results in serial specimens are considered diagnostic of active disease.



The presence of IgM antibodies may be detectable within 2 weeks after the onset of symptoms; however, the antibody may be detected longer than 6 months after infection.


The presence of IgG antibodies parallels the CF antibodies and may suggest an active or a recent asymptomatic infection with Coccidioides immitis/posadasii; however, antibodies may persist after the infection has resolved.


An equivocal result (a band of nonidentity) cannot be interpreted as significant for a specific diagnosis. However, this may be an indication that a patient should be followed serologically.


Over 90% of primary symptomatic cases will be detected by combined immunodiffusion and CF testing.

Report Available

4 to 7 days

Day(s) Performed

Monday through Friday

Clinical Reference

1. Larone D, Mitchell T, Walsh T: Histoplasma, blastomyces, coccidioides, and other dimorphic fungi causing systemic mycoses. In: Murray PR, Baron EJ, Pfaller MA, et al, eds. Manual of Clinical Microbiology. 7th ed. ASM Press; 1999:1260-1261

2. Ramanan P, Wengenack NL, Theel ES: Laboratory diagnosis for fungal infections: a review of current and future diagnostic assays. Clin Chest Med. 2017 Sep;38(3):535-554. doi: 10.1016/j.ccm.2017.04.013

Method Name

Complement Fixation (CF)


Specimen Type


Ordering Guidance

This test is a confirmatory assay for positive screening tests (ie, enzyme immunoassay).


The recommended test to evaluate for possible Coccidioides infection is COXIS / Coccidioides Antibody Screen with Reflex, Serum.

Specimen Required

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1.8 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial.

Specimen Minimum Volume

1.2 mL

Specimen Stability Information

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

Reference Values



If positive, results are titered.




Results are reported as positive, negative, or equivocal.

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

86635 x 3

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SCOC Coccidioides Ab, CompF/ImmDiff, S 87435-4


Result ID Test Result Name Result LOINC Value
8295 Coccidioides Ab, CompF, S 5096-3
21649 Coccidioides, IgG, ImmDiff, S 62459-3
21648 Coccidioides, IgM, ImmDiff, S 62458-5


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

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-CNS-Infections, mml-Pediatric