Summary & Overview
CPT 86666: Ehrlichia Antibody Immunoassay (Serology)
CPT code 86666 denotes a laboratory immunoassay that evaluates a patient’s serum for antibodies to Ehrlichia, a bacterial genus associated with tick-borne infections. Nationally, serologic testing for tick-borne pathogens is a common component of diagnostic workflows for febrile and exposure-related illnesses; accurate coding for these assays supports clinical decision-making and laboratory reporting. 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 assay, typical sites of service, and payer coverage considerations. The publication summarizes reimbursement and billing benchmarks where available, highlights policy and coverage updates affecting laboratory immunoassays, and situates 86666 within clinical testing workflows for suspected Ehrlichia infection. Practical details include typical service contexts, common billing modifiers (listed separately), and guidance on documentation elements typically associated with serologic testing. Data not available in the input is clearly identified in relevant sections.
Billing Code Overview
CPT code 86666 describes an immunoassay performed by a laboratory analyst to evaluate a patient’s serum for antibodies to the bacteria Ehrlichia. This test is a serologic antibody assay used to detect host immune response to Ehrlichia infection.
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Service type: Laboratory immunoassay serology testing
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Typical site of service: Clinical laboratory or hospital laboratory setting
Clinical & Coding Specifications
Clinical Context
A patient presents to an outpatient primary care clinic or infectious disease clinic with fever, headache, myalgias, malaise, and recent history of tick exposure in an endemic area. The clinician documents possible ehrlichiosis after noting thrombocytopenia or elevated liver enzymes on basic labs. A serum sample is collected and sent to the laboratory for immunoassay testing to detect antibodies to Ehrlichia species (CPT 86666). The typical workflow: clinician orders the test, phlebotomy collects serum, specimen is routed to the clinical laboratory, a medical laboratory scientist or immunology technologist performs the immunoassay, verifies results, and the laboratory information system finalizes the report. Results are reviewed by the ordering clinician to confirm diagnosis and guide antimicrobial therapy. Typical sites of service include outpatient clinics, hospital outpatient laboratories, and reference laboratories. Pediatric and adult patients with compatible exposure and symptoms are the usual candidates for this serologic test.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | When billing separates the professional interpretation/reporting from the technical test component for physician services overseeing the assay. |