Summary & Overview
CPT 81346: TYMS Gene Variant Detection, Tandem Repeat
CPT code 81346 covers a molecular pathology laboratory procedure that detects specific variants in the thymidylate synthetase (TYMS) gene, including common tandem repeat variants. This genetic test is clinically relevant for assessing TYMS-related pharmacogenomic profiles and potential implications for chemotherapy sensitivity and dosing. Nationally, CPT code 81346 is part of expanding precision-medicine billing as genomic assays become more integrated into routine oncology and pharmacogenomics care.
Key payers addressed in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise review of coverage context across major national payers, typical sites of service, and the clinical rationale for using TYMS variant testing. The publication summarizes benchmark considerations, common modifiers used with molecular lab services, and policy themes affecting reimbursement and utilization management. The content provides clinical context on what the assay detects, how it is performed in a laboratory setting, and why the test matters for therapeutic decision-making.
Data not available in the input for specific associated taxonomies, ICD-10 diagnosis pairings, and related billing codes is noted where relevant.
Billing Code Overview
CPT code 81346 describes a technical laboratory test that detects specific changes in the thymidylate synthetase (TYMS) gene, focused on common variants such as the tandem repeat variant. The procedure involves laboratory analysis of patient DNA to identify TYMS gene alterations that can inform clinical decision-making related to drug metabolism and targeted therapies.
Service Type: Molecular pathology / genetic testing
Typical Site of Service: Clinical laboratory or reference genetic testing laboratory
Clinical & Coding Specifications
Clinical Context
A 58-year-old patient with stage II colorectal adenocarcinoma undergoing molecular profiling to guide fluoropyrimidine-based chemotherapy selection. The oncologist orders tumor or germline testing to detect common thymidylate synthase gene (TYMS) variants, such as tandem repeat polymorphisms, to assess potential impact on drug response and toxicity. The specimen (formalin-fixed paraffin-embedded tumor tissue or peripheral blood) is collected in the pathology or outpatient infusion center, sent to the molecular diagnostics laboratory. The lab analyst performs technical testing using PCR-based fragment analysis or sequencing to detect TYMS tandem repeat variants. Results are reviewed by a molecular pathologist and reported to the treating oncologist; the professional component covers interpretation and report generation, while the technical component covers specimen handling, reagents, instrumentation, and analysis. Typical sites of service include hospital-based molecular laboratories, independent reference laboratories, and outpatient pathology labs supporting oncology clinics.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the interpretation/reporting portion performed by a pathologist or laboratory physician. |
TC |