Blood Sciences Test

Thiopurine Methyl Transferase (TPMT)


1 x EDTA Blood

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Reference Range

TPMT activity is measured at 37°C, pH 7.4 using 6-thioguanine as the substrate.

(NOTE Units are now mU/L as from 09/08/10, reference ranges have also changed from this date)
DEFICIENT                Less than 10
LOW                                20-67
NORMAL                      68-150
HIGH                        Greater than 150

Test Usage

Assessment of patients who are considering Azothioprine therapy

Other information : TPMT is inducible by thiopurine drugs. If the patient has been receiving azathioprine or 6-mercaptopurine prior to the TPMT assay, the result may be raised above the basal level.


Referred test

Turnaround Time

15 days

Cannot be added on to an existing request

Assayed By

Dept of Chemical Pathology Sandwell & West Birmingham Hospital

Minimum Repeat Interval

There is no need to ever repeat this test

Specimen Labelling Procedure