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.