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.


This test should only be performed for patients currently on thiopurine therapy. This therapy includes administration of azathioprine or mercaptopurine.

This test may not be useful in patients with autoimmune hepatitis.


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
10 - 12 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