Thiopurine Metabolites by LC-MS/MS
Test Mnemonic
THIMET
CPT Codes
- 80299 - QTY (1)
Aliases
- 6-MMP
- 6-TG
Includes
- 6-Thioguanine (6-TG)
- 6-Methylmercaptopurine (6-MMP)
Performing Laboratory
Mayo Clinic Dpt of Lab Med & Pathology
Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 3 mL | Whole blood | EDTA (Lavender) | Refrigerated | Separate specimens must be submitted when multiple tests are ordered. |
Minimum Specimen Requirements
| Volume | Type | Container | Collect Temperature | Transport Temperature | Special Instructions |
|---|---|---|---|---|---|
| 1.5 mL |
Stability
| Environmental Condition | Description |
|---|---|
| Refrigerated | 8 days |
| Ambient | 24 hours |
| Frozen | Unacceptable |
Days Performed
Mon - Sat
Turnaround Time
1 - 5 days
Methodology
| Name | Description |
|---|---|
| Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) |
Special Info
Grossly hemolyzed, lipemic, icteric and clotted specimens will be rejected. This test is New York DOH approved.
Clinical Info
This test is primarily used to verify compliance, optimize therapy, and identify elevated metabolite concentrations that may result in toxicity after initiation of thiopurine drug therapy for the treatment of inflammatory bowel disease. Recommended time points for monitoring include: 4 weeks after starting treatment to verify patient compliance and look for early risk of toxicity; 12 to 16 weeks after starting therapy when 6-thioguanine nucleotides have reached steady-state; and annually. It may also be ordered in patients who do not respond to therapy as expected or as needed for dose changes, flare-ups, signs of toxicity, or suspicion of noncompliance. The test will measure 6-methylmercaptopurine (6-MMP) and 6-thioguanine nucleotides (6-TGN) in erythrocytes. Target 6-thioguanine (6-TGN) concentrations are 235 to 450 pmol/8x10(8) RBC with lower levels suggesting suboptimal dosing and higher levels associated with increased risk of myelotoxicity and leukopenia. High 6-methylmercaptopurine (6-MMP) levels (greater than 5700 pmol/8x10[8] RBC) suggest an increased risk for hepatotoxicity and potentially "thiopurine hypermethylation."