THIOPURINE METHYLTRANSFERASE ACTIVITY

Sub Category

DRUGS/ TDM/ TOXICOLOGY.

Synonyms/Aliases

TPMT PHENOTYPE; TPMT ACTIVITY; TPMT DEFICIENCY; 6-MERCAPTOPURINE (6-MP; PURINETHOL) TOXICITY; AZATHIOPRINE (IMURAN) TOXICITY.

Abbreviations

TPMT.

^Type

INDIVIDUAL TEST.

^{7 DAYS}

RESULTS READY/ REPORTED IN 7 WORKING DAYS.

^Method

LC-MS.

^Temp

REFRIGERATED.

^Setup

BATCHED.

Components Parameters

N/A.

PRE-ANALYTIC CONSIDERATIONS

Test Ordering Instructions

FILL OUT TEST REQUEST FORM FULLY & LEGIBLY.

Patient preparation

COLLECT SAMPLES PRIOR TO INITIATION OF THERAPY WITH THIOPURINE DRUGS.

Sample type

EDTA PLASMA OR HEPARIN PLASMA.

Container/ preservative

EDTA OR HEPARIN WITH ALIQUOTING OF PLASMA INTO A SEPARATION VIAL.

Sample volume

AT LEAST 2 ML.

Rejection criteria

LABELING ISSUE (UNLABELED/ MISLABELED); MISSING REQUEST FORM; MISMATCH BETWEEN REQUEST FORM & SAMPLE DETAILS; MISSING AGE/ GENDER; WRONG SAMPLE TYPE; INSUFFICIENT SAMPLE; FROZEN SAMPLE.

Other Instructions

THE PLASMA SEPARATION VIAL MUST BE LABELED WITH AT LEAST 2 PATIENT IDENTIFIERS AND THE SAMPLE TYPE (E.G. EDTA PLASMA; HEPARIN PLASMA). TESTING SHOULD NOT BE RETROSPECTIVE I.E. AFTER COMMENCEMENT OF THERAPY.

Reference intervals

INTERPRETIVE DATA IS PROVIDED ON THE REPORT.

Clinical Utility

TO DETECT THIOPURINE METHYLTRANSFERASE DEFICIENCY PRIOR TO INITIATION OF TREATMENT WITH THIOPURINE DRUGS E.G. AZATHIOPRINE, 6-MERCAPTOPURINE (6-MP), 6-THIOGUANINE (6-TG) ETC. TPMT DEFICIENCY PREDISPOSES TO MYELOTOXICITY (BONE MARROW TOXICITY) FROM STANDARD DOSES OF THIOPURINE DRUGS. INCREASED TPMT ACTIVITY MAY BE ASSOCIATED WITH RESISTANCE TO THIOPURINE DRUGS & INCREASED RISK OF HEPATOTOXICITY.

Test Limitations/ Confounders

N/A.