Summary & Overview

CPT 86161: Functional Complement Activity Test

CPT code 86161 represents a laboratory test that assesses the functional activity of complement components C1 through C9, used to evaluate immune competence and to help diagnose autoimmune disorders. Nationally, complement functional testing plays a role in infectious disease assessment, immunodeficiency evaluation, and autoimmune disease workups, making it relevant across hospital, reference, and outpatient laboratory settings.

Key payers addressed 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 of service, and the payer landscape covered in the analysis. The publication provides benchmarks where available, coding context, common modifiers, and implications for laboratory billing and claims processing.

This summary equips laboratory managers, billing professionals, and policy analysts with a clear description of the service represented by CPT code 86161, the national payer scope considered, and the types of operational and reimbursement topics explored in the full publication. Data not available in the input is noted where applicable in supporting sections.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare86161CPTcomplement testinglaboratoryimmunologyautoimmuneclinical pathologydiagnostic test

Billing Code Overview

CPT code 86161 describes a laboratory technical procedure that measures the functional activity of complement components (C1 through C9). These functional complement tests evaluate the complement system’s ability to detect and fight infection and help identify autoimmune conditions in which the body produces antibodies against its own cells and tissues.

Service type: Laboratory diagnostic testing (clinical pathology / immunology panel)

Typical site of service: Clinical laboratory or hospital laboratory

Clinical & Coding Specifications

Clinical Context

A 34-year-old female presents to an outpatient immunology clinic with recurrent sinopulmonary infections and a history of autoimmune hemolytic anemia. The ordering clinician requests a functional complement assay to evaluate the activity of the classical and alternative complement pathways (components C1–C9) to assess for complement deficiencies or dysregulation that may explain susceptibility to infection or autoimmune phenomena. Blood is drawn in the clinic phlebotomy area and transported to the hospital clinical laboratory. The laboratory technologist performs a functional complement assay, documents specimen integrity and test controls, runs the assay on the laboratory analyzer, interprets technical results, and generates a report. Results are routed to the ordering immunologist and added to the patient record. Typical sites of service include outpatient hospital laboratory, independent clinical laboratory, and hospital inpatient laboratory when testing is ordered during admission.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when billing only the physician interpretation component separate from the laboratory technical component.
`TC`	Technical component	Use when billing only the laboratory technical component (equipment, technician labor, reagents).
`90`	Reference laboratory	Use when the test is performed by an outside/reference laboratory under contract.
`91`	Repeat clinical diagnostic laboratory test	Use when the same test is repeated on the same day to obtain a valid result.
`22`	Increased procedural services	Use when test required significantly greater resources or complexity than typical and documentation supports a payment adjustment.
`52`	Reduced services	Use when the test is partially performed or fewer elements than described in the code were completed.
`59`	Distinct procedural service	Use when billing indicates a distinct service independent of other services on same day (e.g., separate specimen or distinct clinical indication).
`78`	Return to the operating/procedure room for a related procedure during postoperative period	Generally not applicable but retained for completeness; rarely used with lab testing if tied to same-day procedural return.
`91`	Repeat clinical diagnostic laboratory test	Duplicate of `91` above — use once per claim when applicable.
`90`	Reference laboratory	Duplicate noted above — include once per claim when applicable.

Taxonomy Code	Specialty	Notes
207RC0000X	Allergy & Immunology	Specialists who commonly order complement function testing for immune deficiency and autoimmune disease evaluation.
207L00000X	Clinical Laboratory	Laboratory medicine/pathology professionals who perform and bill for the technical component of the assay.
207H00000X	Hematology	Hematologists who evaluate hemolytic anemias and complement-mediated cytopenias and may order these tests.
2084P0800X	Pediatric Rheumatology	Pediatric specialists who evaluate complement-mediated rheumatologic disorders in children.
208000000X	Internal Medicine	General internists who may order initial immune workups and coordinate testing.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`D80.9`	Immunodeficiency, unspecified	Complement functional testing is used to evaluate suspected primary or secondary immunodeficiency presenting with recurrent infections.
`D69.5`	Secondary thrombocytopenia	Complement-mediated processes can contribute to cytopenias; testing helps assess immune-mediated causes.
`D59.11`	Autoimmune hemolytic anemia, warm antibody type	Complement activation contributes to hemolysis in some cases; functional testing assists diagnosis and management.
`M32.9`	Systemic lupus erythematosus, unspecified	Complement consumption (low function) is common in active SLE and guides disease activity assessment.
`H66.9`	Otitis media, unspecified	Recurrent otitis or sinopulmonary infections may prompt evaluation for complement deficiencies.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`86038`	Antibody; infectious agent, titer, quantitative	Often ordered alongside complement testing when evaluating infection-related immune responses or autoimmune serologies.
`83020`	Ammonia; blood	May be part of broader laboratory panels in acute settings but not commonly directly related; included as supportive metabolic testing when indicated.
`83516`	Protein; total, serum	Frequently ordered concurrently to assess overall protein status and complement protein levels in context.
`82725`	Ferritin; quantitative	Used to evaluate iron stores in patients with chronic inflammation or hemolysis alongside complement testing.
`86162`	Complement component, specific (e.g., C3, C4) quantitation	Often performed in tandem with functional complement assays to identify low component levels that correlate with functional deficiency.