Thiopurine Methyltransferase (TPMT), RBC

Sunquest Code:TPMT  
Epic Code:LAB6987Epic Name:Thiopurine Methyltransferase, RBC
Synonyms:Thiopurine Methyltransferase (TPMT) Enzyme Activity Level; 6-Mercaptopurine
Methodology:Enzymatic/Liquid chromatography/Tandem mass spectrometry
Turnaround Time:Specimens are sent to reference laboratory Mon-Sat; results are reported within 3-4 days.

This test was developed and its performance characteristics determined by ARUP Laboratories. The U.S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

Collection Instructions

Specimen:Whole Blood
Optimal Volume:5 mL
Minimum\Peds Volume:3 mL
Container:Purple (EDTA) (Green (sodium heparin, no gel))
Collection Instructions:Refrigerate within 3 hours of collection.
Causes for Rejection:Gel separator tube. Specimens collected in sodium fluoride/potassium oxalate (gray) tube. Hemolyzed, frozen or room temperature specimens.

Processing and Shipping

Specimen Processing:Do not process. Whole blood. Store in refrigerator. Do not freeze.
Shipping Instructions:Ship at refrigerated temperature.
Stability:Stability: 3 hours at room temperature; 6 days refrigerated.
Test Performed at or Referral Lab Lab Sendouts  (ARUP)
Referral Lab number:92066


Reference Range:

Low TPMT Activity

Less than 17.0 U/mL

Intermediate TPMT Activity

17.0-23.9 U/mL

Normal TPMT Activity

24.0-44.0 U/mL

High TMT Activity

Greater than 44.0 U/mL



Use:Phenotype test to assess risk for severe myelosuppression with standard dosing of thiopurine drugs. Can also detect rapid metabolizer phenotype. Must be performed before thiopurine therapy is initiated.

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