TPMT Genotyping
Also known as: TPMTGENO
Use
This genotyping test assesses genetic risk for severe myelosuppression with standard dosing of thiopurine drugs in individuals for whom thiopurine therapy is being considered or who have had an adverse reaction to thiopurine therapy. Thiopurine drug therapy is used for autoimmune diseases, inflammatory bowel disease, acute lymphoblastic leukemia, and to prevent rejection after solid organ transplant. The inactivation of thiopurine drugs is catalyzed in part by TPMT. Variants in the TPMT gene are associated with an accumulation of cytotoxic metabolites leading to increased risk of drug-related toxicity with standard doses.
Special Instructions
Counseling and informed consent are recommended for genetic testing. Informed consent is required for NY patients. Consent forms are available online. Guidelines for genotype-based dosing are published by the Clinical Pharmacogenetics Implementation Consortium (CPIC) and are available on their website.
Limitations
Only the targeted TPMT variants will be detected by this test. Because the complex TPMT*3A allele contains the variants found in the *3B and *3C alleles, this test cannot distinguish the 3A/negative genotype (intermediate enzyme activity) from the rare *3B/*3C genotype (no or low enzyme activity). Genotyping may reflect donor status in patients who have received allogeneic stem cell or bone marrow transplants within 2 weeks of specimen collection. Actual enzyme activity and expression and risk for adverse reactions to thiopurines may be affected by additional genetic and nongenetic factors not evaluated by this test.
New York Approved
Methodology
PCR-based (PCR)
Biomarkers
LOINC Codes
- 31208-2
- 41048-0
- 36922-3
- 71356-0
- 11526-1
Result Turnaround Time
5-10 days
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
3 mL
Minimum Volume
1 mL
Container
Lavender (EDTA), pink (K2EDTA), or yellow (ACD solution A or B)
Storage Instructions
Refrigerated
Causes for Rejection
Plasma or serum; specimens collected in sodium heparin or lithium heparin; frozen specimens in glass collection tubes; frozen yellow (ACD solution A or B)
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 72 hours |
| Refrigerated | 1 week |
| Frozen | 1 month |