A new clinical guideline from the American Gastroenterological Association (AGA) conditionally recommends reactive therapeutic drug monitoring (TDM) to guide treatment changes in adults with active inflammatory bowel disease (IBD) treated with anti-TNF agents. AGA's Clinical Guidelines Committee reports in Gastroenterology that the recommendation is based on "very low quality of evidence." According to the authors, there were just three observational studies and one randomized controlled trial of patients with IBD on maintenance anti-TNF therapy. The committee said several issues remain unresolved, such as "the optimal timing for measuring trough concentrations." It asserted that, "In most cases, the panel recommends that a trough level for infliximab or adalimumab be drawn as close to the next dose as possible (i.e., within 24 hours). Additionally, while the drug trough concentration is consistent across different commercial assays, assays for anti-drug antibodies are not readily comparable with each other." AGA made no recommendation about the proactive use of routine TDM in adults with quiescent IBD treated with anti-TNF agents due to a "knowledge gap."