Summary & Overview
CPT 80159: Clozapine Level Assay, Therapeutic Drug Monitoring
CPT code 80159 represents a laboratory assay to measure clozapine levels in a patient specimen, a clinically important therapeutic drug monitoring service used to guide dosing and safety for patients on clozapine therapy. Nationally, this code supports management of treatment-resistant schizophrenia and related indications where clozapine monitoring reduces risk of toxicity and guides clinical decisions.
Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. The publication provides a national-level overview of coding context, typical sites of service, and payer coverage patterns. Readers will find concise benchmarks for utilization, an outline of clinical context for when clozapine level testing is relevant, and notes on common billing considerations. Data not available in the input is explicitly noted where applicable.
This summary is intended for billing managers, laboratory directors, payers, and clinicians seeking a clear, policy-focused description of CPT code 80159 and its role in therapeutic drug monitoring programs.
Billing Code Overview
CPT code 80159 describes a laboratory assay performed to determine the level of clozapine in a patient specimen. This service is a therapeutic drug monitoring test used to measure clozapine concentration for clinical management of patients receiving the medication.
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Service type: Laboratory therapeutic drug monitoring
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Typical site of service: Clinical laboratory or hospital laboratory; specimen collection may occur in outpatient clinics or inpatient settings
Clinical & Coding Specifications
Clinical Context
A 38-year-old patient with treatment-resistant schizophrenia is receiving clozapine therapy under a monitored program. Periodic therapeutic drug monitoring is ordered to measure plasma clozapine concentration to assess adherence, efficacy, and risk of toxicity (including agranulocytosis and seizures). A clinician orders the clozapine level test when the patient reports increased sedation, confusion, or new seizures, after dose changes, or to confirm subtherapeutic levels when symptoms recur. A blood specimen is collected in an outpatient laboratory or hospital phlebotomy service, transported to the chemistry/toxicology laboratory, and analyzed using validated immunoassay or chromatography methods. Results are reported to the prescribing psychiatrist and documented in the medical record for dose adjustment and safety monitoring.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
90 | Reference (Outside) Laboratory | Use when the specimen is tested by an outside reference lab and only the performing lab bills. |
TC | Technical Component | Use when billing for the technical component only (laboratory performs analysis; professional interpretation not billed separately). |