Thiopurine metabolites-13580

Test info

Thiopurine metabolites
6MP metabolites
6TG metabolites
Azathioprine metabolites
Mercaptopurine metabolites

LabCorp's Thiopurine Metabolites assay measures the red-cell concentration of 6-MMP (formed from 6-MP by thiopurine methyltransferase) and also measures the concentration of the resulting 6-TG after removal of the mono-, di-, or tri-phosphates from the various 6-thioguanine nucleotides.


EDTA whole blood
3.0 mL
1.0 mL
Submission of the minimum volume does not allow for repeat testing

Immediately following collection, mix sample thoroughly by gently inverting 8 - 10 times, to prevent clotting


Lavender (EDTA), 4mL


Refrigerated (preferred) - 8 days

Ambient - 1 day

Frozen - NO

  • Frozen specimen
  • Specimens other than EDTA whole blood
  • Gross hemolysis


Esoterix Endocrinology (803800) via LabCorp (503800): R-LC
4 - 10 days

Whole blood washing and red blood cell harvesting/counting.

Liquid chromatography/tandem mass spectrometry (LC/MS-MS) after acidic hydrolysis

Clinical and Interpretive info


For treatment of inflammatory bowel disease (IBD)*
Suboptimal dosing:
            <235 pmol 6-TGN/8×108 red blood cells
Optimal dosing:
          235−450 pmol 6-TGN/8×108 red blood cells
Increasing risk for myelotoxicity and leucopenia :
        >450 pmol 6-TGN/8×108 red blood cells
Hepatotoxicity risk:  >5700 pmol 6-MMPN/8×108 red blood cells


Once thiopurine therapy has been undertaken and an equilibrated drug level is achieved (usually 3 to 6 months), literature suggest that the measurement of thiopurine metabolites is warranted in the following situations:

  1. Unresponsive patients to rule out:
    1. patient non-compliance (low 6-MMP and low 6-TG in those not taking medications),
    2. those with diversion of metabolites away from 6-TG production (low 6-TG and normal or increased 6-MMP),
    3. those with refractory to treatment (adequate 6-TG but lack of clinical response), and
    4. those with excessive 6-MMP (or increased 6-MMP:6-TG ratio with adequate 6-TG) leading to increased hepatotoxicity.
  2. Clinically responsive patients to look for excessive levels of either 6-MMP or 6-TG to avoid toxicity.


Result 32660-3