TPMT Genotyping

Casandra

Casandra Test Code AR69637Version 1 (DRAFT)

Performing Lab

Lab ARUP LaboratoriesLab Test ID 3017372CPT Code 81335

Also known as: TPMTGENO

Clinical Use

Order Test

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.

Test Details

New York Approved

Methodology

PCR-based (PCR)

Biomarkers

9 targets

TPMTTPMTTPMTTPMTTPMTTPMTTPMTTPMT+1 more

LOINC Codes

Result Codes

31208-2
41048-0
36922-3
71356-0
11526-1

Result Turnaround Time

5-10 days

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)