Summary & Overview

CPT 86635: Coccidioides Antibody Immunoassay (Blood or CSF)

CPT code 86635 represents a laboratory immunoassay to detect antibodies to the fungus Coccidioides in blood or cerebrospinal fluid. This serologic test is an important diagnostic tool for identifying coccidioidomycosis, a fungal infection that can cause pulmonary and disseminated disease. Nationally, accurate laboratory testing for Coccidioides supports appropriate clinical management, surveillance, and public health response.

Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise overview of the clinical purpose of the test, typical sites where the service is performed, and the common billing modifiers associated with lab services. The publication also summarizes what readers can expect in related content: reimbursement benchmarks, coding guidance, billing considerations, and clinical context for test utilization.

This summary frames CPT code 86635 for a national audience, providing the clinical definition and payer scope. Data not available in the input is noted where applicable in detailed sections. The following sections present benchmarks, policy updates, and coding details that help billing professionals and laboratory managers understand how this immunoassay is applied in practice and reimbursed across major payers.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare86635CPTfungal serologycoccidioidomycosislaboratoryimmunoassayblood testingcerebrospinal-fluiddiagnostic-testing

Billing Code Overview

CPT code 86635 describes an immunoassay performed by a laboratory analyst to detect antibodies to the fungus Coccidioides in a patient's blood or cerebrospinal fluid (CSF). This test identifies serologic evidence of coccidioidomycosis (Valley fever) and supports clinical diagnosis when fungal infection is suspected.

Service type: Laboratory serologic testing (fungal antibody immunoassay)

Typical site of service: Clinical laboratory or hospital laboratory (specimens collected in outpatient clinics, emergency departments, or inpatient settings and processed in a lab).

Clinical & Coding Specifications

Clinical Context

A patient presents to an outpatient laboratory or hospital clinical laboratory with symptoms of a systemic or pulmonary fungal infection — for example, fever, cough, weight loss, night sweats, arthralgia, or a progressive respiratory illness in a person who lives in or has traveled to endemic areas for Coccidioides (Valley fever). The ordering clinician (infectious disease specialist, pulmonologist, emergency physician, or primary care provider) requests serologic testing to detect IgM and/or IgG antibodies to Coccidioides in serum or cerebrospinal fluid when disseminated disease or meningitis is suspected.

The typical workflow: the clinician orders the test; a phlebotomist collects blood (serum) or a provider collects cerebrospinal fluid during lumbar puncture; the specimen is transported to the laboratory with appropriate labeling and requisition. A laboratory technologist or immunology specialist performs the immunoassay (enzyme immunoassay or other FDA-cleared method) and interprets results. Results are returned to the ordering provider, often with reflex testing recommendations (e.g., complement fixation, culture, or repeat serology) documented in the lab report. Common sites of service include outpatient laboratories, hospital inpatient laboratories, emergency departments, and ambulatory clinics where phlebotomy is performed.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when billing only the professional (interpretation) portion if the laboratory charges are split between technical and professional components.
`TC`	Technical component	Use when billing only the technical portion (performing the assay, equipment, supplies) and the professional interpretation is billed separately.
`90`	Reference (outside) laboratory	Use when the specimen is sent to an outside reference laboratory and the reporting laboratory is not performing the test locally.
`91`	Repeat clinical diagnostic test	Use when the same test is repeated on the same patient within a short time period to confirm results or monitor a trending marker per payer rules.
`59`	Distinct procedural service	Use when another unrelated procedure or service is performed on the same day and documentation supports separate reporting.
`52`	Reduced services	Use if the test cannot be completed as ordered and only partial testing or limited procedures are performed.
`53`	Discontinued procedure	Use if the specimen could not be obtained (e.g., failed CSF collection) and the service was discontinued.
`76`	Repeat procedure by same physician or other qualified health care professional	Use when the identical test is repeated on the same day by the same provider because of an issue with the initial specimen.
`90`	Reference laboratory (duplicate listed to emphasize commonality)	Use when sending testing to an external lab; some payers require `90` for external lab claims.
`91`	Repeat clinical diagnostic laboratory test (duplicate to emphasize use)	Use when repeating the immunoassay to verify an unexpected result.

Taxonomy Code	Specialty	Notes
207Q00000X	Infectious Disease	Specialists who order and interpret fungal serologies for complex cases.
207RC0000X	Pulmonology	Pulmonologists evaluate respiratory presentations and often order Coccidioides testing.
207L00000X	Pathology & Laboratory Medicine	Laboratory directors and clinical pathologists oversee test performance and quality.
208D00000X	Emergency Medicine	Emergency physicians may order the test in acute presentations prior to admission.
207RC0006X	Allergy & Immunology	Allergists/immunologists evaluate immune responses and may order serologic testing in systemic presentations.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`B38.0`	Coccidioidomycosis, unspecified	Primary diagnosis for acute or chronic coccidioidal infection; serology is used to support diagnosis.
`B38.1`	Pulmonary coccidioidomycosis	Pulmonary presentations often prompt serum testing for Coccidioides antibodies.
`B38.2`	Coccidioidomycosis, disseminated	Disseminated disease (skin, bones, CNS) requires serologic testing and further evaluation.
`B38.3`	Coccidioidomycosis, cutaneous	Cutaneous manifestations may be associated with positive serology for systemic involvement.
`B38.4`	Coccidioidal meningitis	When meningitis is suspected, CSF or serum antibody testing for Coccidioides is indicated.
`R50.9`	Fever, unspecified	Non-specific symptom that may trigger infectious workup including fungal serology.
`R05`	Cough	Respiratory symptom commonly present in pulmonary coccidioidomycosis prompting testing.
`Z20.828`	Contact with and (suspected) exposure to other viral communicable diseases	Used in exposure evaluation; may be applied when recent travel or exposure to endemic areas is documented.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`86635`	Antibody; Coccidioides (immunoassay)	Primary immunoassay used to detect antibodies to Coccidioides in serum or CSF.
`86664`	Antibody; Histoplasma capsulatum (immunoassay)	Other fungal serology that may be ordered in the differential diagnosis of endemic mycoses.
`86661`	Antibody; Blastomyces dermatitidis (immunoassay)	Alternative fungal serology for differential diagnosis of systemic/mycotic infections.
`87070`	Culture, bacterial; any source, other than blood, aerobic with isolation and presumptive identification of isolates	May be performed when attempting to culture respiratory or other specimens for fungal pathogens as part of the workup.
`87077`	Culture, fungal, any source, with isolation and presumptive identification	Fungal culture that can be ordered alongside serology when direct organism detection is indicated.
`36556`	Collection of blood specimen from a central venous catheter	Procedure code relevant when blood for serology is drawn from an indwelling catheter rather than peripheral venipuncture.