Summary & Overview

CPT 86671: Immunoassay for Fungal Antibodies

CPT code 86671 represents an immunoassay laboratory test used to detect antibodies to a specific fungal organism when no more specific CPT code exists. This test is clinically important for diagnosing or supporting the diagnosis of fungal infections that are not covered by targeted assay codes. It affects clinical laboratories, hospital labs, infectious disease clinicians, and payers because it informs diagnostic workups for suspected fungal disease and can influence downstream care decisions.

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 code’s clinical role, typical sites of service, and the service type. The publication outlines common billing modifiers associated with laboratory services and identifies areas where payers frequently apply medical necessity and documentation policies. It also summarizes how CPT code 86671 fits into laboratory coding workflows and where this nonspecific fungal antibody assay is used in clinical practice.

This summary does not include state-level policy differences. Data not available in the input: associated taxonomies, specific ICD-10 diagnoses, related billing codes, payer-specific coverage rules, and service-line financial benchmarks.

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Billing Code Overview

CPT code 86671 describes an immunoassay to detect antibodies in a patient’s blood directed against a specific fungus when that fungal target is not covered by a more specific CPT code. The service is a laboratory serologic test used to evaluate immune response to fungal pathogens.

Service type: Laboratory — serology / immunology test

Typical site of service: Clinical laboratory or hospital laboratory

Clinical & Coding Specifications

Clinical Context

A 45-year-old outpatient presents to an infectious disease clinic with several weeks of persistent cough, low-grade fevers, and unexplained weight loss after travel to an endemic region. The treating clinician suspects a systemic or pulmonary mycosis not covered by more specific serologic tests. A phlebotomy draw is performed and sent to the hospital reference laboratory. The laboratory analyst performs an immunoassay to detect antibodies to a specific fungus that does not have a more specific CPT code, reported as 86671. Results are routed back to the ordering clinician via the electronic medical record. Typical workflow: clinician documents clinical suspicion (history, imaging), places the order for the non-specific fungal antibody immunoassay, patient blood is collected in the outpatient lab or phlebotomy station (Typical Site of Service: outpatient clinic or ambulatory laboratory), specimen is transported to the clinical laboratory, the immunoassay is run by the lab analyst, and the lab issues a result with interpretive comment for the clinician to integrate into diagnosis and management decisions. Typical patient scenarios include suspected rare systemic fungal infections, indeterminate serology for common fungi, or when initial more specific tests are negative but clinical suspicion persists. Billing follows lab reporting rules with the laboratory as the performing facility and the ordering provider as the clinician of record.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when reporting only the physician/clinical interpretation portion of the lab test if split billing applies.
`TC`	Technical component	Use when reporting only the laboratory technical component (equipment, technician labor, reagents).
`90`	Reference (outside) laboratory	Use when the specimen was sent to a separate reference laboratory for performance of the assay.
`91`	Repeat clinical diagnostic laboratory test	Use when the same assay is repeated on the same day on the same patient to obtain a valid result.
`52`	Reduced services	Use if testing was partially performed or a limited service was rendered.
`53`	Discontinued procedure	Use if specimen collection or testing was started but discontinued for documented medical reasons.
`59`	Distinct procedural service	Use when a separate and distinct lab service is performed the same day and must be differentiated from other services.
`90`	Reference (outside) laboratory	Use when the performing laboratory is an external entity (listed to show common applicability).
`91`	Repeat test (same day)	Use when an assay is repeated to confirm or validate an unexpected result.
`22`	Increased procedural services	Use when the laboratory documents substantially greater resources expended to complete the test (rare for standardized immunoassays).
`78`	Return to operating/procedure room	Not typically used for this lab test; included for completeness when a patient returns for a related procedure.
`59`	Distinct procedural service	Use to indicate a separate lab procedure when multiple tests are billed the same day.
`90`	Reference laboratory	Use to indicate testing done by a separate laboratory entity.
`91`	Repeat clinical diagnostic lab test	Use when a repeat run is medically necessary to confirm results.

Taxonomy Code	Specialty	Notes
207Q00000X	Infectious Disease Specialist	Orders and interprets fungal serology for systemic mycoses.
207L00000X	Pathology and Laboratory Medicine	Oversees laboratory testing, quality control, and result validation.
363A00000X	Clinical Laboratory Scientist	Performs immunoassays and documents technical component.
2080P0207X	Pulmonology	May order testing for suspected pulmonary fungal infections.
208000000X	Internal Medicine	Primary care or hospitalist ordering initial serologic evaluation.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`B44.9`	Aspergillosis, unspecified	Fungal infections such as aspergillosis may prompt fungal antibody testing when presentation is atypical.
`B38.9`	Coccidioidomycosis, unspecified	Serologic testing for coccidioidal antibodies is a related clinical scenario; `86671` may be used when no specific code fits.
`B39.9`	Histoplasmosis, unspecified	Histoplasma exposure and compatible symptoms often prompt fungal serology in evaluation of systemic mycosis.
`B48.9`	Other mycoses, unspecified	Used when clinical suspicion is for a less common fungus not represented by a specific CPT-coded assay.
`A49.9`	Bacterial infection, unspecified	Sometimes sequelae or differential includes bacterial infection; lab testing suite may include broad infectious workup.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`87070`	Culture, bacterial; any other source, other than blood, with isolation and presumptive identification of isolates	May be ordered when fungal culture from respiratory or tissue specimens is pursued alongside serologic testing.
`87210`	Smear, gram or other staining procedure, by technician, for bacteria, fungi, or other organisms	May be performed on clinical specimens as an initial rapid diagnostic adjunct to serology.
`87102`	Culture, fungal, other than dermatophyte, with isolation and presumptive identification of isolates	Performed when definitive organism identification by culture is indicated in suspected fungal infection.
`84443`	Assay of thyroid stimulating hormone (TSH)	Example of other laboratory tests that may be ordered concurrently for general evaluation; not specific to fungal disease but commonly part of workup.
`87471`	Infectious agent detection by nucleic acid (DNA or RNA); organism-specific, amplified probe technique	Molecular testing on specific pathogens may be ordered when available and clinically indicated as confirmatory testing following non-specific serology.