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.
Lavender (EDTA), 4mL
Refrigerated (preferred) - 8 days
Ambient - 1 day
Frozen - NO
Whole blood washing and red blood cell harvesting/counting.
Liquid chromatography/tandem mass spectrometry (LC/MS-MS) after acidic hydrolysis
For treatment of inflammatory bowel disease (IBD)*
<235 pmol 6-TGN/8×108 red blood cells
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: