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 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.


Ambient: 72 hours; Refrigerated: 1 week; Frozen: 1 month


Polymerase Chain Reaction (PCR)/Fluorescence 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

81335; 81306


Component Test Code* Component Chart Name LOINC
2012240 TPMT Predicted Phenotype 36922-3
3001536 TPMT2 Specimen 31208-2
3001537 TPMT Genotype 41048-0
3001538 NUDT15 Genotype 93194-9
3001539 TPMT2 Interpretation 50398-7
3016872 NUDT15 Phenotype 93194-9
3016873 EER TPMT and NUDT15 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
  • nudix
  • NUDT15 mutation
  • S-adenosyl-L-methionine genotype
  • Thioguanine
  • Thiopurine
  • Thiopurine S-methyltransferase genotype
  • TPMT genetics
  • TPMT mutation