Introduction: The commercial availability of drug concentration and antibody testing for anti-TNF therapy promises optimized drug dosing and informed therapeutic decision-making for patients with inflammatory bowel disease (IBD). However, there is no consensus on how to interpret the results for various clinical scenarios. We applied the RAND/UCLA appropriateness method toward establishing the appropriateness of how to act upon results of anti-TNF concentration and antibody testing. Methods: A comprehensive, structured literature review was conducted on the topic of drug concentration and anti-drug antibodies in patients with Crohn’s disease (CD) and ulcerative colitis (UC) for all approved anti-TNF therapies. This review was presented to an expert panel including clinician and pharmacist experts who have published on the topic, and the building research in inflammatory bowel disease globally (BRIDGe) group, a globally diverse panel of 13 gastroenterologists experienced in IBD treatment and therapeutic drug monitoring. A total of 143 clinical scenarios addressed the appropriateness of various strategies in response to test results. Panelists used a modified Delphi method to anonymously rate each scenario through a web-based questionnaire, and then met in-person to discuss and anonymously re-rate appropriateness on a 1-9 scale (1-3 inappropriate, 4-6 uncertain, 7-9 appropriate). Disagreement was assessed using a validated index. Results: Interpretation of anti-TNF drug concentration and antibody levels was rated based on different clinical scenarios including at the end of induction therapy in primary non-responders, at the end of induction in responders, in secondary non-responders, and at a time point during the first year of maintenance therapy. Panelists established the appropriateness of various clinical management options including changing therapy within-class, switching out of class, adjusting drug dose/interval, adding/adjusting concomitant immunomodulators, and “doing nothing” for each of 6 permutations of high/low drug concentration and high/low/undetectable antibody levels. A mobile app was then developed allowing easy access and display of how to respond to various permutations of drug concentration and antibody level in the setting of specific clinical settings. Conclusion: The appropriate response to anti-TNF drug and antibody testing for IBD was determined through a modified delphi panel based on expert interpretation of the available literature. The time to test and clinical action on the results is highly dependent on the specific clinical scenario. These recommendations can be accessed using a new mobile app to guide clinicians towards optimized anti-TNF therapy. Disclosure - Dr. Melmed- Consultant: Abbvie, Janssen.Dr. Irving- Consultant: Abbvie. Dr. Jones- Consultant: Abbvie, UCB. Dr. Kaplan- Consultant: Abbvie, UCB. Dr. Kozuch- None. Dr. Velayos-Consultant: Janssen. Dr. Baidoo- None. Dr. Sparrow-Consultant: Abbvie. Dr. Bressler- Consultant: Abbvie, UCB. Dr. Cheifetz- Consultant: Abbvie. Janssen, UCB. Dr. Devlin- Consultant: Abbvie, Janssen, UCB. Dr. Harrell- Consultant: Abbvie. Dr. Casteelle-Consultant: Janssen, Abbvie. Dr. Mould- Consultant: Abbvie, Janssen, Prometheus. Dr. Dubinsky- Consultant: Abbvie, Janssen, UCB, Prometheus. Dr. Colombel-Consultant: Abbvie, Janssen, UCB. Dr. Sandborn- Consultant: Abbvie, Janssen, UCB, Prometheus. Dr. Siegel- Consultant: Abbvie, Janssen, UCB, Prometheus. This research was supported by an industry grant from Janssen, Abbvie, UCB.