CPT 87320: Chlamydia trachomatis Antigen Immunoassay
CPT code 87320 identifies an immunoassay for detection of Chlamydia trachomatis antigens, a laboratory test used to diagnose active chlamydial infection. Nationally, this code matters because Chlamydia remains a common sexually transmitted bacterial infection and timely laboratory diagnosis guides treatment and public health interventions. The code captures antigen-based testing methods such as enzyme immunoassay (EIA) rather than nucleic acid amplification testing (NAAT).
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find clinical context about when antigen immunoassays are used, the typical site of service (clinical or hospital laboratory), and how this CPT code fits into diagnostic workflows. The publication outlines benchmarking elements and policy-relevant considerations affecting coverage and billing practice for antigen detection methods versus other testing modalities. It also highlights common billing modifiers and notes where input data were unavailable.
The piece is intended for laboratory managers, billing professionals, and policy analysts seeking a concise national overview of CPT code 87320, its clinical purpose, and the payer landscape relevant to antigen-based Chlamydia testing.
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Billing Code Overview
CPT code 87320 describes a laboratory immunoassay performed by a lab analyst to detect antigens of Chlamydia trachomatis, typically using techniques such as enzyme immunoassay (EIA). This service is categorized as a diagnostic microbiology test intended to identify active infection by detecting bacterial antigens.
Service type: Laboratory diagnostic test (microbiology — antigen detection)
Typical site of service: Clinical laboratory or hospital laboratory
Data not available in the input for payers, associated taxonomies, ICD-10 diagnoses, and related codes.
Clinical & Coding Specifications
Clinical Context
A sexually active adult female presents to an outpatient primary care clinic with new onset dysuria and mucopurulent cervical discharge following unprotected intercourse. The clinician performs a focused sexual health history and pelvic exam, collects an endocervical swab, and sends the specimen to the clinical laboratory for antigen detection of Chlamydia trachomatis using an immunoassay (e.g., enzyme immunoassay). The laboratory analyst performs 87320 to detect C. trachomatis antigen, documents specimen adequacy and test performance, and reports positive or negative results to the ordering clinician for treatment decisions and partner notification. Typical workflow includes specimen accessioning, assay setup, controls verification, result interpretation, and release into the electronic medical record. Typical sites of service are outpatient clinics, urgent care centers, sexual health/STI clinics, and hospital laboratories performing routine diagnostic testing.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
00 | No modifier | General billing when no modifier applies |
11 | Provider's usual, most frequently performed service | Use when this service is the primary, routine lab test performed by the billing provider |
26 | Professional component | Use when billing only for the professional interpretation component (rare for immunoassay, may apply in split-billing arrangements) |
TC | Technical component | Use when billing only for the technical component of the test (laboratory performs assay but a separate provider bills for professional component) |
90 | Reference (outside) laboratory | Use when the specimen was sent to an outside reference laboratory for testing |
QK | Ordering/Referring provider | Use to identify the ordering/referring provider when required by payer reporting |
QX | Ordering/Rendering provider modifier | Use when the ordering provider also performs the service under applicable payer rules |
QY | Ordering/Prescribing provider | Use when applicable for lab billing to identify the ordering prescriber per payer rules |
52 | Reduced services | Use when the test was partially performed or limited compared to the full procedure |
53 | Discontinued procedure | Use when the test was started but discontinued for patient safety or specimen issues |
90 | Reference (outside) laboratory | Use when testing is performed by an outside lab; see payer-specific reporting |
| Taxonomy Code | Specialty | Notes |
|---|---|---|
| 208000000X | Pathology | Clinical laboratory and anatomic pathology oversight and laboratory directors commonly associated with 87320 |
| 207RC0000X | Obstetrics & Gynecology | OB/GYN clinicians frequently order chlamydia antigen testing for symptomatic women and screening |
| 208000000S | Clinical Laboratory | Laboratory technologists and analysts performing immunoassays and reporting results |
| 207Q00000X | Family Medicine | Primary care and urgent care providers commonly order STI testing |
| 2086S0122X | Diagnostic Molecular Laboratory | Laboratories performing immunoassays and molecular diagnostics; oversight and technical staff |
Related Diagnoses
| ICD-10 Code | Description | Clinical Relevance |
|---|---|---|
A56.0 | Chlamydial infection of lower genitourinary tract | Direct indication for testing with 87320 to detect C. trachomatis antigen |
A56.1 | Chlamydial infection of pelvic organs | Relevant when pelvic inflammatory disease is suspected and chlamydia testing is required |
N34.1 | Urethritis, unspecified | Male or female urethral symptoms prompt chlamydia testing |
N72 | Inflammation of cervix (cervicitis) | Cervical mucopurulent discharge is an indication for chlamydia antigen testing |
Z11.3 | Encounter for screening for infections with a predominantly sexual mode of transmission | Asymptomatic screening for chlamydia uses antigen or molecular testing |
Related CPT Codes
| CPT Code | Description | Relationship to This Procedure |
|---|---|---|
87491 | Infectious agent antigen detection by immunoassay technique, qualitative or semiquantitative, multiple-step method for Chlamydia trachomatis | Alternative chlamydia antigen assay code that may be used depending on payer rules and assay method |
87492 | Infectious agent antigen detection by immunoassay technique, qualitative or semiquantitative, multiple-step method for Chlamydia trachomatis; performed with simultaneous testing for Neisseria gonorrhoeae | Used when combined antigen testing for C. trachomatis and N. gonorrhoeae is performed from the same specimen |
87850 | Infectious agent detection by immunoassay for multiple organisms, screening; qualitative | May be used for multiplex immunoassay panels that include C. trachomatis antigen among other targets |
87480 | Infectious agent antigen detection by immunoassay technique for Neisseria gonorrhoeae | Often ordered concurrently with chlamydia testing in symptomatic patients or screening encounters |
36415 | Collection of venous blood by venipuncture | Commonly performed during STI evaluation when serologic testing (e.g., HIV, syphilis) is ordered alongside 87320 |