Test Category: Specialist Biochemistry
Investigation Name:Thiopurine S-Methyltransferase Enzyme Activity (TPMT)
Alias or Abbreviation:TPMT (phenotype/activity)
Accreditation:Extension for scope, awaiting accreditation due to relocation.
Intro:
Thiopurine drugs, such as mercaptopurine and azathioprine, 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, which in effect reduces concentrations of the active metabolite, 6-thioguanine nucleotides (6TGN).
TPMT activity exhibits autosomal co-dominant polymorphism.
In a Caucasian population approximately 89% have normal enzyme activity, 11% low activity and 0.3% undetectable levels (deficient).Measurement of TPMT activity prior to starting thiopurine drugs is recommended and allows dosing of thiopurine drugs to be adjusted appropriately.
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.
TPMT genotype analysis will be performed to confirm TPMT status for selected samples – go to ‘TPMT genotype’ page for further details.
Pathology Laboratory:TPMT Laboratory
Requestable Seperately?Yes
Units:mU/L
Minimum Sample Volume:2mL
Expected Turnaround Time:3 working days
Test Code:TPMT
Sample Type:
EDTA/lithium heparin whole blood (NB: lithium heparin samples are not suitable for genotype analysis)Complex Reference Range:Deficient < 10 mU/L
Potential deficient 10-19 mU/L
Low 20 - 67 mU/L
Normal 68 - 150 mU/L
High >150 mU/L
Collection Conditions / Other Information:Please send unseparated.
Stable for 6 days at room temperature and up to 14 days at 4°C.
Samples older than 14 days at receipt will not be analysed.
Samples > 8 days on receipt are reported with a comment to highlight the age of sample.
Recent blood transfusions (within 120 days) may give misleading results. Provide details of recent transfusions on the request form.
Please provide details of liver transplant.
Referred to Another Laboratory?No
Storage Requirements:Do not freeze, store at 4°C prior to dispatch. Please send unseparated.
Posting Address / Requirements:1st Class post, ambient temperature.
Sandwell Health Campus,
Specialist Chemistry,
Pathology Department,
Lyndon,
B71 4HJ
NPEX / PDF Reporting Available:Yes
EQA Scheme:We participate in an interlaboratory sample exchange.
Equalis: 527- TPMT genotype, phenotype and thiopurine metabolites.
Further information:- Before taking a sample for TPMT activity, patients should be advised that DNA confirmation may be performed, and patients must give consent for genetic testing prior to sample collection.
Please indicate on request form if patient has had blood transfusion in last 90 days, samples from patients who have received a recent blood transfusion can give misleading results.
TPMT should be measured BEFORE starting on thiopurine drugs.
- Renal impairment can cause false elevations in TPMT activity.
Lead Contact Details:Consultant Clinical Scientist, Dr Hayley Sharrod-Cole,
Email: hayley.sharrod-cole@nhs.net
Email Address For Chasing Results:rwh-tr.bcpsspecialistchemistryenquiries@nhs.net
Methodology:Measured by by HPLC.
Site Sample Tested:Sandwell Health Campus
Cost:Email: bcpspathology.info@nhs.net for further details
Contact Number:0121 507 5162
