Thiopurine Methyltransferase (TPMT) Enzyme
thiopurine methyltransferase, thiomethytransferase, 6 mercaptopurine
Test Codes
EPIC: LAB10144, Beaker: XTMPT, ARUP #92066
Department
Send Outs
Instructions
This test is used to detect those individuals with low TPMT (approximately 10% of the population) who will have excessive and potentially lethal myelosuppression when given standard doses of azathioprine
or 6-MP.
Specimen Collection Criteria
Collect (preferred specimen): One Dark Green-top Lithium or Sodium Heparin tube.
Also acceptable: One Lavender-top EDTA tube.
Physician Office/Draw Specimen Preparation
Do not centrifuge. Refrigerate (2-8°C or 36-46°F) specimens in original collection tube immediately after collection.
Preparation for Courier Transport
Transport: 4.0 mL whole blood, refrigerated (2-8°C or 36-46°F). (Minimum: 3.0 mL)
Rejection Criteria
- Frozen specimen.
- Hemolyzed specimen.
- Gel separator tubes
- Room temp specimen.
- Specimens not collected and processed as indicated.
In-Lab Processing
Do not centrifuge. Refrigerate (2-8°C or 36-46°F) specimens in original collection tubes immediately after collection.
Transport: 4.0 mL whole blood, refrigerated (2-8°C or 36-46°F). (Minimum: 3.0 mL)
Storage
Specimen Stability for Testing:
Room Temperature (20-26°C or 68-78.8°F): 3 hours
Refrigerated (2-8°C or 36-46°F): 6 days
Frozen (-20°C/-4°F or below): Unacceptable
Specimen Storage in Department Prior to Disposal:
Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.
Laboratory
Sent to ARUP Laboratories, Salt Lake City, UT.
Performed
Sunday – Saturday.
Results available in 3-5 days.
Reference Range
By report.
Test Methodology
Enzymatic/Quantitative Liquid Chromatography – Tandem Mass Spectrometry (LC-MS/MS).
Interpretation
By report.
Clinical Utility
Azathioprine (Imuran) and 6-Mercaptopurine (6-MP, Perinethol) are thiopurine drugs that are used to treat neoplasms and a variety of rheumatologic, dermatologic, or neurologic diseases in which the immune system is thought to play a role. Although thiopurines are very useful drugs, they are also potentially toxic. The metabolic conversion of azathioprine and 6-MP to purine nucleotides and their subsequent incorporation into DNA is important in its therapeutic efficacy but also plays a role in its toxicity. The enzyme thiopurine methyltransferase (TPMT) inactivates these thiopurines by thiol methylation. A balance is established between competing metabolic pathways such that sufficient drug is converted to the active antimetabolite for therapeutic efficacy but not so much as to lead to myelotoxicity (bone marrow suppression).
CPT Codes
84433
Contacts
Send Outs Laboratory – RO
248-551-9045
Name: Send Outs Laboratory – RO
Location:
Phone: 248-551-9045
Last Updated
9/23/2024
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