Test Overview
Clinical Utility
6-Mercaptopurine (Purinethol) and its imidazolyl derivative, Azathioprine (Imuran), are immunosuppressive drugs. 6-Mercaptopurine (6-MP) is indicated for remission induction and maintenance therapy of acute lymphoblastic leukemia (ALL). Azathioprine is indicated as an adjunct for the prevention of rejection in renal allograft (kidney transplant) patients, for the management of rheumatoid arthritis, and for the management of inflammatory bowel disease.
Azathioprine is cleaved to 6-MP. 6-MP is metabolized via a series of enzymatic steps to 6-thioguanine nucleotides (6-TGNs), to 6-methyl-mercaptopurine (6-MMPNs) by the enzyme thiopurine methyltransferase (TPMT), and to 6-thiouric acid by the enzyme xanthine oxidase (XO). TPMT enzyme activity has large inter-individual variations which affect the efficacy, toxicity and variability of the treatment. Therapeutic drug monitoring of 6-MP metabolites (6-TGNs and 6-MMPNs) in erythrocytes is recommended to assist therapy, particularly in combination with TPMT enzyme activity or mutation analysis.
Method
Liquid chromatography-tandem mass spectrometry (LC-MS/MS)
Result Included
6-Thioguanine (6-TG); 6-Methylmercaptopurine (6-MMP)
Aliases/Synonyms
6-Methylmercaptopurine; 6-MMP; 6-MP; 6-Thioguanine; 6-TG; Azathioprine Metabolites
Specimen
Specimen Type
Whole BloodContainers
Collection Containers
Lavender top (EDTA)
Volume
Sample Volume
5 mL
Minimum Volume
2.5 mL
Collection & Handling
Collection Instructions
Collect a trough specimen (within 1 hour prior to next dose).
Handling Information
Keep specimen cold – do not freeze. Due to limited stability, specimen must be received at ICL Monday to Wednesday within 3 days of collection.
Stability
| Ambient | Refrigerated | Frozen |
|---|---|---|
| 24 hours | 7 days | Unacceptable |
Rejection Criteria
| Criteria | Specification |
|---|---|
| Hemolysis | Gross |
| Specimen | Heparin Tube |
Performance & Interpretation
Turnaround Time
8 days
Results
-
6-TGpmol/8x10(8) RBC235 - 400
-
6-MMPpmol/8x10(8) RBC< 5700
Comment
These results are useful in assessing a patient's metabolism of azathioprine (AZA) or 6-mercaptopurine (6-MP). A 6-thioguanine (6-TG) level greater than 235 pmol/8x10(8) RBC has been associated with remission and very high levels have been associated with leucopenia. 6-methylmercaptopurine (6-MMP) levels greater than 5700 pmol/8x10(8) RBC may be associated with hepatoxicity.
Referral Location
Out-of-Country
Interface & Setup
HL7 Interface Codes
| Order Code | Result Name | Result Codes | Units |
|---|---|---|---|
| THIOP WB | 6 TG | 64566 | pmol/8x10(8)RBC |
| 6 MMP | 64567 | pmol/8x10(8)RBC |
Test Version
Last Updated
2023-04-05