Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
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 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.
Specimen container paediatric:
EDTA whole blood
Specimen container adult:
EDTA whole blood
Minimum volume paediatric:
4 mL
Minimum volume adult:
4 mL
Sample stability:
Process up to 14 days from sample collection
Add on test:
[email protected] (external)
Interpretation:
*TPMT activity between 10 – 19 mU/L may indicate undisclosed blood transfusion of deficient patient or poor sample storage.
Reference ranges:
TPMT status:
Deficient activity <10*
Low Activity 20 – 67*
Normal Activity 68 – 150
High Activity >150
*TPMT activity between 10 – 19 mU/L may indicate undisclosed blood transfusion of deficient patient or poor sample storage.
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 will be performed to confirm the patient’s TPMT status.
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 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