Summary & Overview
CPT 81335: TPMT Gene Variant Detection, Molecular Diagnostic
CPT code 81335 denotes a molecular diagnostic laboratory service detecting common variants in the thiopurine S–methyltransferase (TPMT) gene, such as *2 and *3. This pharmacogenetic test matters nationally because TPMT genotype influences thiopurine drug metabolism and dosing decisions across oncology, gastroenterology, and rheumatology, affecting patient safety and medication efficacy. Labs and payers consider this code for coverage, clinical validity, and appropriate use criteria.
Key payers covered in typical analyses include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find an overview of the clinical context for TPMT variant testing, common sites of service, and payer landscape considerations. The publication summarizes standard benchmarks for laboratory billing and reimbursement for genetic testing, highlights policy and coding guidance relevant to molecular diagnostics, and outlines points for coding compliance and documentation. It also provides clinical background on why TPMT variant detection is ordered and how results are applied in medication management.
Data not available in the input for some fields such as associated taxonomies, specific ICD-10 diagnoses, and related codes.
Billing Code Overview
CPT code 81335 describes a laboratory test in which a lab analyst performs the technical procedures to detect specific genetic variants in the thiopurine S–methyltransferase (TPMT) gene, commonly including variants such as *2 and *3. This test identifies genetic changes that can affect metabolism of thiopurine medications and informs clinical interpretation of TPMT-related pharmacogenomic results.
Service Type: Genetic molecular diagnostic testing (TPMT variant detection)
Typical Site of Service: Clinical laboratory or molecular diagnostics laboratory
Clinical & Coding Specifications
Clinical Context
A 12-year-old patient with newly diagnosed acute lymphoblastic leukemia (ALL) is scheduled to start thiopurine-based therapy (mercaptopurine or azathioprine). Before initiating therapy, the oncologist orders genetic testing to assess thiopurine S‑methyltransferase (TPMT) gene variants to identify poor, intermediate, or normal metabolizer status. A peripheral blood sample is collected at an outpatient laboratory or hospital outpatient phlebotomy unit and sent to a molecular diagnostics laboratory. The laboratory analyst performs 81335 to detect common TPMT variants (for example, *2, *3) using validated genotyping methods. Results are reported to the ordering provider and entered into the electronic health record; the oncology team uses results to guide thiopurine dosing or consider alternative therapies. Typical sites of service include outpatient hospital laboratories, independent reference laboratories, and hospital-based molecular pathology laboratories.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the professional (interpretation) component if the lab separates technical and professional components. |
TC |