Observational Study Evaluating the Effectiveness of Drug Concentration to Predict the Recapture of Response in Crohn's Disease Patients With Loss of Response ( PRADA )

* Documented diagnosis of Crohn's Disease. * Treatment with adalimumab, for a minimum of 16 weeks, as per clinical practice, at a dose of 160 mg at week 0, 80 mg at week 2, and then 40 mg q2w with a documented response as defined by the investigator. * Current evidence of active inflammatory disease/LOR defined as the presence of active inflammation (confirmed with a CRP ≥ 5 mg/L and/or a fecal calprotectin ≥ 250µg/g. * Ability of subject to participate fully in all aspects of this clinical trial. * Written informed consent must be obtained and documented.

* Primary non-responders to 16 weeks of adalimumab therapy. * Received any investigational drug within the 16 weeks of adalimumab therapy. * Serious underlying disease other than CD that, in the opinion of the investigator, may interfere with the subject's ability to participate fully in the study. * History of alcohol or drug abuse that, in the opinion of the investigator, may interfere with the subject's ability to comply with the study procedures. * Stools positive for Clostridium difficile. * Pregnant or lactating women. * Current enrolment in any other interventional research study. * Presence of perianal or abdominal abscess.