TPMT

Pathology category

Biochemistry - referred tests

Code

TPMT

Referral code

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Test information

Thiopurine drugs are widely used to treat inflammatory and autoimmune disease, leukaemia and to prevent rejection post organ transplant. These drugs are catabolised to inactive metabolites by TPMT. Measurement of TPMT activity is recommended before prescribing these drugs. Patients with undetectable TPMT activity are generally not treated with thiopurine drugs due to increased risk of severe side effects. In patients with high activity, an increased dose may lead to accumulation of inactive metabolites and increased risk of hepatotoxicity

Guidelines

Pre-analytical

Samples from patients who have received a recent blood transfusion can give misleading results. Repeat tseting not usually indicated.

Reference range

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

Tube type

Tube type info

EDTA (Li Hep can be used for TPMT activity)

Special requirements

Whole Blood

Minimum volume

2mL

Assay frequency

TAT Inpatient (urgent)

TAT Inpatient

2 weeks

TAT GP/Outpatient

2 weeks

Referral lab

Clinical Biochemistry City Hospital Birmingham