Summary & Overview
CPT 80157: Free Carbamazepine Assay
CPT code 80157 identifies a lab test that measures the free (unbound) concentration of carbamazepine in a patient specimen. This measurement is clinically important because the free fraction represents the active portion of the drug and can guide therapeutic drug monitoring, dose adjustments, and safety assessments for patients treated for epilepsy and other neurologic or psychiatric conditions. Nationally, assays for free anticonvulsant levels inform clinical management and have implications for lab service utilization and payer coverage policies.
Key payers discussed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise review of the code’s clinical context, typical site of service, and common billing modifiers. The publication highlights what clinicians and billing professionals need to know about where this service is performed, why free-level testing differs from total drug level testing, and how payers commonly approach laboratory toxicology and therapeutic drug monitoring services.
The report provides benchmarks and policy-relevant context where available, summarizes typical use cases in therapeutic drug monitoring, and notes missing input fields when necessary. Data not available in the input will be identified explicitly in relevant sections.
Billing Code Overview
CPT code 80157 describes a laboratory assay performed by a lab analyst to measure the free (unbound) concentration of carbamazepine in a patient specimen. Carbamazepine is an anticonvulsant medication used in the treatment of epilepsy and certain neurologic and psychiatric disorders; the free fraction represents the pharmacologically active portion not bound to proteins or other constituents.
Service Type: Clinical laboratory testing — therapeutic drug monitoring (free drug assay)
Typical Site of Service: Clinical laboratory or hospital laboratory
Data not available in the input.
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.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | When billing for the physician interpretation component if applicable (rare for automated lab analytes). |