CPT code 84433 represents a laboratory test that measures thiopurine S–methyltransferase (TPMT) levels in blood. TPMT testing is clinically important because reduced enzyme function increases the risk of myelosuppression in patients treated with thiopurine medications such as azathioprine, mercaptopurine, and thioguanine. Nationally, TPMT testing informs medication selection and dosing to reduce serious hematologic adverse events and is increasingly part of precision prescribing workflows.

Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. The publication gives readers a concise overview of how CPT code 84433 is used, typical sites of service, and clinical rationale for testing. It summarizes payer coverage patterns and common billing considerations relevant to laboratory services for pharmacogenetic and enzyme assays.

Readers will learn clinical context for TPMT testing, operational details for ordering and specimen handling, and typical billing and service-line placement for laboratory enzyme assays. Where available, benchmarks and policy highlights outline payer coverage approaches and common administrative issues. Data not available in the input is noted where applicable.