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    v1.0.30
    OpenPayerBilling CodesAntimicrobial Susceptibility StudiesCPT cpt-87181-antimicrobial-susceptibility-gradient-diffusion-test
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    CPT 87181: Antimicrobial Susceptibility Test, Gradient Diffusion

    CPT code 87181 describes a laboratory antimicrobial susceptibility test in which a lab analyst performs the technical steps to evaluate a culture isolate’s sensitivity to a specific antibiotic using a gradient diffusion test device placed on an agar plate; service type: microbiology susceptibility testing (gradient diffusion/MIC determination); typical site of service: clinical microbiology laboratory or hospital lab where cultured isolates are processed and tested.

    For related coverage guidance, see recent payer policy updates: Biomarker Testing for Autoimmune Rheumatic Disease, Immunopharmacologic Monitoring of Therapeutic Serum Antibodies, Immune Cell Function Assay.

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    Clinical & Coding Specifications

    Clinical Context

    A typical patient is an adult hospitalized with a bloodstream infection or complicated urinary tract infection where an isolate (bacterial or fungal) has been cultured from blood, urine, wound, or other sterile site. The microbiology lab receives the culture isolate and the lab analyst performs an antimicrobial susceptibility test using a gradient diffusion device (e.g., Etest) placed on an agar plate inoculated with the isolate to determine the minimum inhibitory concentration (MIC) for a specific antibiotic. The workflow begins with organism identification (often by MALDI-TOF or biochemical testing), followed by selection of appropriate antibiotics to test based on organism and clinical history, setup of the gradient diffusion strip on the inoculated plate, incubation, and reading of the MIC at the point where the ellipse of inhibition intersects the strip. Results are documented in the laboratory information system and communicated to the ordering clinician for targeted antimicrobial therapy adjustments. Typical sites of service include hospital clinical microbiology laboratories, independent diagnostic laboratories, and outpatient reference labs that process culture isolates sent from clinics and hospitals.

    Related CPT Codes

    CPT CodeDescriptionRelationship to This Procedure
    87070Culture, bacterial; any other source, except blood, aerobic, with isolation and presumptive identification of isolatesOften performed before susceptibility testing to isolate and presumptively identify the organism to select appropriate antibiotics for 87181.
    87077Culture, bacterial; quantitative colony count, urineUrine culture that may provide the isolate subsequently tested with 87181 for antibiotic susceptibility.
    87491Infectious agent detection by nucleic acid (DNA or RNA); organism(s) detected by probe, each organismMolecular identification tests often performed prior to or instead of culture; results can guide which susceptibility tests like 87181 are indicated.
    87449Infectious agent antigen detection by immunoassay, single step method; Streptococcus, group ARapid antigen tests may prompt culture and subsequent susceptibility testing when treatment failure or complications occur.
    88305Surgical pathology, gross and microscopic examinationNot typically performed by microbiology but may be part of the clinical workflow for infected tissue where isolates are obtained for 87181.

    Related Modifiers

    6 rows

    ModifierDescriptionWhen to Use
    26Modifier 26 (Professional Component) identifies and bills only the professional portion of a split service — the physician’s interpretation, report, and medical judgment — when the technical…- Use CPT Modifier -26 when you are billing only the professional component (PC) of a split‑bill eligible service—i.e., you performed the physician interpretation, medical judgment and prepared a…
    59Modifier 59 indicates a distinct procedural service when two procedures that are not normally billed together are clinically and procedurally separate. The CPT definition (as reiterated by CMS)…- Use modifier -59 to report a distinct procedural service when documentation supports that the procedure reported is not normally billed together with another service on the same day because of a…
    62Modifier 62 indicates that two surgeons function as co‑surgeons, each performing distinct parts of the same primary surgical procedure. It is appended to the primary procedure code (and any…- Use modifier -62 when two surgeons act as co‑surgeons (both primary surgeons) on a single definitive primary procedure, each performing distinct parts of the same surgical procedure (append -62 to…
    76Modifier -76, Repeat Procedure or Service by Same Physician or Other Qualified Health Care Professional, is appended when the same provider performs an identical, medically necessary procedure or…- Use modifier -76 when the same physician or other qualified health care professional performs an identical procedure or service a second (or subsequent) time on the same date of service and the…
    90Modifier ‑90 (Reference/Outside Laboratory) indicates that a laboratory test was performed by an entity other than the treating or reporting provider. The American Medical Association defines…- Use CPT modifier -90 when a laboratory test is performed by an outside/reference laboratory (an entity other than the treating or reporting physician or qualified professional) and the claim needs…
    91Modifier 91 — “Repeat Clinical Diagnostic Laboratory Test” — is appended when the exact same CPT laboratory test is performed more than once for the same patient on the same day because serial,…- Use modifier 91 when the exact same CPT laboratory test is performed more than once on the same patient on the same date because serial or repeated testing is medically necessary to monitor…

    Related Provider Taxonomies

    8 rows

    Taxonomy Code
    207RH0000X
    207L00000X
    174400000X
    363A00000X
    3336C0004X
    207WX0108X
    372600000X
    3336C0002X

    Related Payer Policy Updates

    Specialty: Immunology/Rheumatology1 / 3

    10 rows

    PolicyPayerEffective Date
    Biomarker Testing for Autoimmune Rheumatic DiseaseOscar Health2026-10-01
    Immunopharmacologic Monitoring of Therapeutic Serum AntibodiesOscar Health2026-10-01
    Immune Cell Function AssayOscar Health2026-10-01
    Biomarker Testing for Autoimmune Rheumatic DiseaseBlue Cross Blue Shield - New Mexico2026-09-04
    Inflammatory Conditions - Orencia Intravenous Preferred Specialty Management Policy for Legacy Prescription Drug ListsCigna2026-09-01
    Secukinumab (Cosentyx) — intravenous (Medicare Advantage)blue cross blue shield - louisiana2026-09-01
    Intravenous Immune Globulin (IVIG) — indications and authorization criteriaBlue Cross Blue Shield - Iowa2026-08-28
    Infliximab Intravenous Products Preferred Specialty Management PolicyCigna2026-08-15
    Kineret (anakinra) — Coverage CriteriaBlue Cross Blue Shield - Iowa2026-08-14
    Actimmune (interferon gamma-1b) — Prior Authorization and Coverage Criteriameridian_health_plan_of_michigan2026-08-01

    Related Codes

    CPT-87182-MULTIPLEX-CARBAPENEMASE-IMMUNOASSAY

    CPT 87182: Multiplex Carbapenemase Immunoassay

    CPT-87183-CARBAPENEM-RESISTANCE-GENE-DETECTION-PER-ISOLATE

    CPT 87183: Detection of Carbapenem Resistance Genes, Per Isolate

    CPT-87184-ANTIMICROBIAL-SUSCEPTIBILITY-DISK-DIFFUSION

    CPT 87184: Antimicrobial Susceptibility by Disk Diffusion (up to 12 agents)

    CPT-87185-ANTIMICROBIAL-ENZYME-DETECTION-SUSCEPTIBILITY-TEST

    CPT 87185: Antimicrobial Susceptibility Enzyme Detection

    CPT-87186-ANTIMICROBIAL-SUSCEPTIBILITY-TESTING-DILUTION-METHODS

    CPT 87186: Antimicrobial Susceptibility Testing by Dilution Methods

    CPT-87187-MLC-ANTIMICROBIAL-SUSCEPTIBILITY-TESTING

    CPT 87187: Minimum Lethal Concentration (Antimicrobial Susceptibility)

    CPT-87188-ANTIMICROBIAL-SUSCEPTIBILITY-MACROBROTH-DILUTION

    CPT 87188: Macrobroth Dilution Antimicrobial Susceptibility Test

    CPT-87190-MYCOBACTERIA-PROPORTION-METHOD-SUSCEPTIBILITY-TESTING

    CPT 87190: Mycobacteria Susceptibility Testing, Proportion Method

    CPT-87197-BACTERIAL-TITER-ANTIBIOTIC-SUSCEPTIBILITY

    CPT 87197: Bacterial Titer for Antibiotic Susceptibility

    Frequently Asked Questions

    References

    1. 1.CPT® Codes and Descriptions. AAPC. Retrieved Aug 11, 2026.Maintains the CPT code set's official descriptions and guidelines, licensed from the American Medical Association, used as the definitional source for CPT codes on this page.
    2. 2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's quarterly release of HCPCS Level II codes and short/long descriptors, the source for HCPCS code definitions and update history.
    3. 3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's complete ICD-10-CM diagnosis code list, used to cross-reference diagnosis codes associated with this procedure or service.
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