Therapeutic drug monitoring methods are lacking for methotrexate (MTX), an immunomodulator used in Inflammatory Bowel Disease (IBD) treatment, alone or in conjunction with infliximab (IFX). Although studies demonstrate a lack of relationship between MTX plasma concentrations and efficacy/toxicity, recent studies in rheumatoid and juvenile idiopathic arthritis suggest a positive correlation between therapeutic response and accumulation of intracellular MTX metabolites, MTX polyglutamates (MTX-Glu).