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TPMT Activity : 18831
Test CodeTHIOMR or 18831
Alias/See Also
Thiopurine Methyltransferase, RBC
CPT Codes
84433
Preferred Specimen
4 mL whole blood collected in each of two EDTA (lavender-top) tubes
Minimum Volume
2 mL (x2)
Instructions
Collect venous blood in 2 separate EDTA (lavender-top) tubes (4 mL each tube). Ship at 2-8°C (refrigerated) within 24 hours of collection. Blood is collected prior to azathioprine (Imuran) or 6-mercaptopurine (6-MP, Purinethol) therapy for screening purposes. The draw time is at the physician's discretion.
Transport Temperature
Refrigerated
Specimen Stability
Ambient: 48 hours
Refrigerated: 9 days
Frozen: Unacceptable
Refrigerated: 9 days
Frozen: Unacceptable
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis. Clotted. Animal specimen. Forensic specimen.
Methodology
Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)
Setup Schedule
Sunday - Thursday
Report Available
4-6 days (From receipt at performing laboratory)
Limitations
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Reference Range
>12 Normal metabolizer
4-12 Intermediate metabolizer
< 4 Poor metabolizer
4-12 Intermediate metabolizer
< 4 Poor metabolizer
Clinical Significance
Help prevent hepatotoxicity from thiopurine therapy. This test helps identify individuals at increased risk of hepatotoxicity from thiopurine dose escalation. Patients with a TMPT activity of 4-12 nmol 6-MMP/hr/mL RBC (heterozygote/low metabolizer) are at increased risk and may require a lower dose of thiopurine drug.
Performing Laboratory
Quest Diagnostics
