Newcastle Laboratories

Thiopurine methyltransferase (TPMT), whole blood

Clinical Background:

Measurement of TPMT activity prior to starting thiopurine drugs is now recommended.
Patients with undetectable TPMT activity are generally not treated with thiopurine drugs due to increased risk of ...

Measurement of TPMT activity prior to starting thiopurine drugs is now recommended.
Patients with undetectable TPMT activity are generally not treated with thiopurine drugs due to increased risk of severe side effects, e.g., myelosuppression. Those with low activity usually receive a reduced dose. In patients with high activity, an increased dose may lead to accumulation of inactive metabolites and increased risk of hepatotoxicity.

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Test Details

  • Discipline:

    Haematology

    Haematology

  • Specimen Container Adult:

    EDTA whole blood

    EDTA whole blood

  • Specimen Container Paediatric:

    EDTA whole blood

    EDTA whole blood

  • Minimum Volume Adult:

    0.5 mL 

    0.5 mL 

  • Minimum Volume Paediatric:

    0.5 mL 

    0.5 mL 

  • Sample Stability:

    4 days at room temperature

    4 days at room temperature

  • Reference Ranges:

    Whole blood TPMT activity (mU/L):
    Deficient < 10
    Low 20 - 67
    Normal 68 - 150
    High >150

    N.B. TPMT activity 10 – 19 mU/L may be seen in TPMT deficient patients who have been transfused.

    Whole blood TPMT activity (mU/L):
    Deficient < 10
    Low 20 - 67
    Normal 68 - 150
    High >150

    N.B. TPMT activity 10 – 19 mU/L may be seen in TPMT deficient patients who have been transfused.

  • Factors Affecting Result:

    Samples from patients who have received a recent blood transfusion can give misleading results. Please provide details of recent transfusions (within 90 days) on the request form and genotyping wil...

    Samples from patients who have received a recent blood transfusion can give misleading results. Please provide details of recent transfusions (within 90 days) on the request form and genotyping will be performed to confirm the patient’s TPMT status. 

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  • Other Info:

    Before taking a sample for TPMT activity, patients should be advised that DNA confirmation may be performed. The only known implication for the genetic variation in TPMT expression is intolerance t...

    Before taking a sample for TPMT activity, patients should be advised that DNA confirmation may be performed. The only known implication for the genetic variation in TPMT expression is intolerance to thiopurine drugs.


    TPMT genotyping (ARMS-PCR) is used to confirm patient TPMT status for selected samples:
    • Deficient TPMT activity
    • Recent blood transfusion
    • Previous severe reaction to thiopurine drugs
    • Change in TPMT status on repeat testing
    Screen for the common TPMT mutations TPMT*2 and TPMT*3

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  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

Availability:

Sample sent to an external laboratory for analysis

Turn Around:

2 weeks

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