Ordering Recommendation

Use this genotyping test to assess genetic risk for severe myelosuppression with standard dosing of thiopurine drugs in individuals for whom thiopurine therapy is being considered or who have had an adverse reaction to thiopurine therapy. This test may be performed irrespective of whether thiopurine therapy is currently being administered.

For enzyme phenotyping prior to thiopurine treatment, refer to Thiopurine Methyltransferase, RBC (0092066). For thiopurine dosing optimization, refer to Thiopurine Metabolites in Red Blood Cells (3016503).

New York DOH Approval Status

This test is not New York state approved.

Specimen Required

Patient Preparation

Lavender (EDTA), pink (K2EDTA), or yellow (ACD solution A or B).

Specimen Preparation

Transport 3 mL whole blood. (Min: 1 mL)

Storage/Transport Temperature


Unacceptable Conditions

Plasma or serum; specimens collected in sodium heparin or lithium heparin; frozen specimens in glass collection tubes; frozen yellow (ACD solution A or B)


Room temperature: 72 hours; Refrigerated: 1 week; Frozen: 1 month


Polymerase Chain Reaction (PCR)/Flourescence Monitoring




5-10 days

Reference Interval

By report

Interpretive Data

Refer to report.

Counseling and informed consent are recommended for genetic testing. Consent forms are available online.

Compliance Category

Laboratory Developed Test (LDT)


Whole blood is the preferred specimen. Saliva samples that yield inadequate DNA quality and/or quantity will be reported as inconclusive if test performance does not meet laboratory-determined criteria for reporting.

Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
2012238 TPMT Genotype Specimen 31208-2
2012239 TPMT Genotype 41048-0
2012240 TPMT Predicted Phenotype 36922-3
3017393 TPMT Interpretation 71356-0
3017394 EER TPMT 11526-1
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • 6-mercaptopurine
  • 6-MP
  • 6-TG
  • 6-thioguanine
  • AZA toxicity
  • Azathioprine
  • nucleoside diphosphate linked moiety X
  • S-adenosyl-L-methionine genotype
  • Thioguanine
  • Thiopurine
  • Thiopurine S-methyltransferase genotype
  • TPMT genetics
  • TPMT mutation
TPMT Genotyping