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    v1.0.30
    OpenPayerBilling CodesTherapeutic Drug AssaysCPT cpt-80157-free-carbamazepine-assay
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    CPT 80157: Free Carbamazepine Quantitative Assay

    CPT code 80157 describes a laboratory quantitative assay of free carbamazepine in a patient specimen, measuring the unbound fraction of the anticonvulsant medication; this is a clinical toxicology/drug monitoring service performed by a laboratory analyst using specialized testing methods. The service type is therapeutic drug monitoring / toxicology testing and the typical site of service is a clinical laboratory or hospital laboratory where specimens are processed and analyzed for medication management and monitoring.

    For related coverage guidance, see recent payer policy updates: Long-Acting Injectable Antiretroviral Agents for HIV, B-Hemolytic Streptococcus Testing, Human Immunodeficiency Virus (HIV) — Coverage Criteria for Testing and Resistance Assays.

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    Clinical & Coding Specifications

    Clinical Context

    A 34-year-old patient with a history of focal epilepsy presents for therapeutic drug monitoring after a recent change in dose of carbamazepine due to breakthrough seizures and symptoms suggestive of toxicity (dizziness, ataxia). The clinician orders a laboratory measurement of the free (unbound) carbamazepine concentration to assess pharmacologically active drug levels because hypoalbuminemia, drug interactions, or other factors may alter protein binding and total drug concentrations. A phlebotomy technician collects a serum specimen, which is sent to the clinical chemistry laboratory. A laboratory analyst performs the technical assay corresponding to 80157 to quantify free carbamazepine; results are reported to the ordering clinician and incorporated into medication management decisions. Typical site of service is an outpatient clinical laboratory, hospital clinical laboratory, or anatomic pathology/chemistry lab within an acute care facility. The service type is a laboratory quantitative therapeutic drug monitoring assay (pharmacologic/therapeutic drug level test) performed by the clinical laboratory technical staff.

    Related CPT Codes

    CPT CodeDescriptionRelationship to This Procedure
    80157Therapeutic drug assay, carbamazepine, freePrimary procedure—quantitative measurement of unbound carbamazepine in serum.
    80155Therapeutic drug assay; carbamazepine (total)Often ordered alongside 80157 to compare total vs free drug concentrations and assess protein binding.
    80053Comprehensive metabolic panel (CMP)Provides albumin and liver function tests that influence carbamazepine protein binding and metabolism; commonly ordered with therapeutic drug monitoring.
    84460Assay of serum or plasma lithium (if relevant)Not directly related pharmacologically but an example of commonly ordered therapeutic drug assays in psychiatry; used when multiple mood stabilizers are monitored concurrently.
    36415Collection of venous blood by venipunctureThe specimen collection CPT code typically performed prior to the laboratory assay.

    Related Modifiers

    5 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…
    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…
    52Modifier ‑52 (Reduced Services) indicates that a service or procedure was partially reduced or omitted at the provider’s discretion, allowing reporting of the basic procedure number with a qualifier…- Use modifier -52 when a physician or qualified health professional electively reduces or omits part of a procedure or service (for example, performing fewer required views or omitting a portion of…
    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…

    Related Provider Taxonomies

    8 rows

    Taxonomy Code
    207RC0000X
    207L00000X
    208D00000X
    2084N0400X
    207QA0505X
    156F00000X
    385HR2055X
    2279E1000X

    Related Payer Policy Updates

    Specialty: Infectious Disease1 / 3

    10 rows

    PolicyPayerEffective Date
    Long-Acting Injectable Antiretroviral Agents for HIVColorado Rocky Mountain Health Plans2026-10-01
    B-Hemolytic Streptococcus TestingOscar Health2026-10-01
    Human Immunodeficiency Virus (HIV) — Coverage Criteria for Testing and Resistance AssaysOscar Health2026-10-01
    Hepatitis Testing (A, B, C, D) Coverage CriteriaOscar Health2026-10-01
    Lyme Disease Testing Coverage CriteriaOscar Health2026-10-01
    Pathogen Panel TestingOscar Health2026-10-01
    Diagnostic Testing of Common Sexually Transmitted InfectionsOscar Health2026-10-01
    Coronavirus Testing in the Outpatient SettingOscar Health2026-10-01
    Testing for Vector-Borne InfectionsOscar Health2026-10-01
    Testing for Diagnosis of Active or Latent TuberculosisOscar Health2026-10-01

    Related Codes

    CPT-80143-ACETAMINOPHEN-QUANTITATIVE-SERUM-ASSAY

    CPT 80143: Acetaminophen Quantitative Assay

    CPT-80145-ADALIMUMAB-LEVEL-ASSAY-THERAPEUTIC-DRUG-MONITORING

    CPT 80145: Adalimumab Quantitative Drug Level Assay

    CPT-80150-AMIKACIN-QUANTITATIVE-ASSAY-THERAPEUTIC-DRUG-MONITORING

    CPT 80150: Amikacin Quantitative Serum Level

    CPT-80151-AMIODARONE-QUANTITATIVE-SERUM-ASSAY

    CPT 80151: Amiodarone Quantitative Drug Level Assay

    CPT-80155-CAFFEINE-LEVEL-TESTING

    CPT 80155: Caffeine Level Quantification

    CPT-80156-CARBAMAZEPINE-TOTAL-LEVEL-LAB-ASSAY

    CPT 80156: Carbamazepine Total Level (Serum)

    CPT-80158-CYCLOSPORINE-QUANTITATIVE-ASSAY-LAB

    CPT 80158: Cyclosporine Quantitation, Laboratory

    CPT-80159-CLOZAPINE-LEVEL-ASSAY-THERAPEUTIC-DRUG-MONITORING

    CPT 80159: Clozapine Level Measurement

    CPT-80161-CARBAMAZEPINE-EPOXIDE-QUANTITATIVE-ASSAY

    CPT 80161: Carbamazepine 10,11-Epoxide Level, Quantitative

    CPT-80162-DIGOXIN-TOTAL-THERAPEUTIC-DRUG-MONITORING

    CPT 80162: Total Digoxin Level in Serum

    Showing 1–10 of 87

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    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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