6-Methylmercaptopurine; 6-MMP; 6-MP; 6-Thioguanine; 6-TG; Azathioprine Metabolites
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Thiopurine Metabolites, Whole Blood
Test ID: THIOP WB
Test
Aliases/Synonyms
Method
Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)
Report Includes
6-Thioguanine (6-TG); 6-Methylmercaptopurine (6-MMP)
Specimens
Whole Blood
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.
Test Location
Quest Diagnostics, California USA
Test Version
5-Apr-2023
Specimen
Specimens
Whole Blood
Collection Containers
Lavender top (EDTA)
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 | 24 hours |
|---|---|
| Refrigerated | 7 days |
| Frozen | Unacceptable |
Rejection Criteria
| Hemolysis | Gross |
|---|---|
| Specimen | Heparin Tube |
Test Version
5-Apr-2023
Performance / Interpretation
Method
Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)
Turnaround Time
8 days
Results
| Name | Units | Reference Range | Conversion Factor | |
|---|---|---|---|---|
| 6-TG | pmol/8x10(8) RBC |
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| 6-MMP | pmol/8x10(8) RBC |
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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.
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Test Location
Quest Diagnostics, California USA
Test Version
5-Apr-2023
Interface / Setup
HL7 Interface Codes
| Order Code | Result Codes | Units |
|---|---|---|
| THIOP WB | 645666 TG | pmol/8x10(8)RBC |
| 645676 MMP | pmol/8x10(8)RBC |
Test Version
5-Apr-2023