Summary & Overview

CPT 86638: Immunoassay for Antibodies to Coxiella burnetii

CPT code 86638 represents a laboratory immunoassay used to detect antibodies to Coxiella burnetii, the bacterium responsible for Q fever. This serologic assay is clinically important for diagnosing acute and chronic Q fever and guiding appropriate clinical management, particularly in febrile illnesses with relevant exposure history. Nationally, accurate laboratory coding for infectious disease serologies supports surveillance, appropriate reimbursement, and consistent clinical documentation.

Key payers included in the review are Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise explanation of the test’s clinical role, typical site of service, and the common modifiers associated with laboratory services. The publication outlines what to expect in payer coverage policies, common billing modifiers, and how this code fits within laboratory service lines.

This summary provides benchmarks and policy context relevant to payers and billing professionals, clarifies the clinical context for ordering clinicians, and highlights areas where coding clarity matters for claims processing. Data not available in the input is noted where applicable.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare86638CPTLaboratorySerologyInfectious DiseaseQ FeverImmunoassayClinical Laboratory

Billing Code Overview

CPT code 86638 describes an immunoassay test performed by a laboratory analyst to detect antibodies to Coxiella burnetii, the bacterium that causes Q fever. The procedure involves laboratory analysis of a patient’s blood specimen to evaluate immune response markers specific to this pathogen.

Service Type: Laboratory diagnostic test — serology (immunoassay)

Typical Site of Service: Clinical laboratory or hospital laboratory

Data not available in the input.

Clinical & Coding Specifications

Clinical Context

A 42-year-old livestock farm worker presents to a primary care clinic with a 2-week history of fever, severe headache, and atypical chest pain. The clinician orders serologic testing for Q fever due to occupational exposure to goats and sheep and an acute febrile illness. A phlebotomy technician draws a blood sample and the specimen is sent to the clinical laboratory. In the lab, a medical laboratory scientist performs an immunoassay to detect antibodies to Coxiella burnetii. Results are reported to the ordering provider and entered into the electronic medical record. If results are equivocal or to determine phase-specific titers, the laboratory may reflex to additional serologic testing or send confirmatory testing to a reference laboratory. Typical site of service is an outpatient clinic, hospital outpatient laboratory, or independent clinical diagnostic laboratory. Turnaround time varies from same day to several days depending on need for confirmatory testing.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when billing only the professional interpretation component if separated from the technical service by the laboratory or referring entity.
`TC`	Technical component	Use when billing only the technical component (laboratory testing, equipment, and supplies) without professional interpretation.
`90`	Reference lab	Use when the service is performed by a reference laboratory on behalf of the reporting laboratory.
`91`	Repeat clinical diagnostic laboratory test	Use when the same test is repeated on the same day to obtain multiple test results for the same patient.
`59`	Distinct procedural service	Use when this test is performed on a separate specimen or encounter distinct from other billed services.
`52`	Reduced services	Use when the test is partially reduced or not fully performed for clinical reasons.
`53`	Discontinued procedure	Use when specimen collection or testing was started but discontinued for clinical or technical reasons.
`23`	Unusual anesthesia	Rarely applicable; use only if unusual anesthesia related to specimen collection was required and reported.
`22`	Increased procedural services	Use when work required to perform the test is substantially greater than normally required (rare for standard immunoassays).
`59`	Distinct procedural service	(Note: `59` duplicated in source list; listed once above.)
`90`	Reference lab	(Note: `90` duplicated in source list; listed once above.)

Taxonomy Code	Specialty	Notes
207Q00000X	Clinical Laboratory Scientist/Medical Technologist	Performs and oversees immunoassays and serologic testing.
207L00000X	Clinical Laboratory Technician	Performs specimen processing and routine assay procedures under supervision.
207K00000X	Clinical Laboratory Director	Physician or doctoral-level director responsible for laboratory testing quality and reporting.
208D00000X	Family Medicine	Ordering clinicians in outpatient settings who request testing for suspected Q fever.
208000000X	Internal Medicine	Hospital and outpatient internists who evaluate febrile illnesses and order relevant serologies.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`A78`	Q fever	Direct disease caused by Coxiella burnetii; primary indication for serologic testing.
`A41.9`	Sepsis, unspecified organism	Used when systemic infection suspected and Q fever is in the differential diagnosis.
`R50.9`	Fever, unspecified	Common presenting symptom prompting serologic testing for causes including Q fever.
`J06.9`	Acute upper respiratory infection, unspecified	Respiratory symptoms can accompany Q fever; used when presentation is nonspecific.
`I39`	Endocarditis in diseases classified elsewhere	Chronic Q fever can present with endocarditis; serology used in evaluation.
`B99`	Other and unspecified infectious diseases	Generic code used when a specific infectious agent has not yet been identified.
`Z20.828`	Contact with and (suspected) exposure to other viral communicable diseases	Adapted for documenting occupational exposure risk factors; used to document possible exposure in certain workflows.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`86638`	Antibodies to Coxiella burnetii; immunoassay, qualitative or semiquantitative	Primary code describing performance of the immunoassay for Q fever antibodies in the laboratory.
`86639`	Antibodies to Coxiella burnetii; confirmatory (e.g., immunofluorescence)	Commonly performed as a confirmatory or reflex test when initial immunoassay is reactive or equivocal.
`36415`	Collection of venous blood by venipuncture	Specimen collection code typically used for obtaining the blood sample sent for the assay.
`99000`	Handling and/or conveyance of specimen to laboratory (non-covered)	May be used by some facilities for specimen handling logistics (coverage varies by payer).
`85025`	Complete blood count (CBC) with automated differential	Often ordered in parallel to evaluate leukocytosis or other hematologic abnormalities in febrile patients.
`87070`	Culture, bacterial; any other source except urine, blood or stool, aerobic, each organism isolated	May be ordered in the diagnostic workup of febrile patients to identify bacterial co-infections.