Prospective, Multicenter Study on the Association Between Serum Ustekinumab Levels and Clinical, Biological and Endoscopic Remission in Patients With Crohn's Disease.

The present study aims to evaluate the association between serum levels (trough) of Ustekinumab and clinical, biological, endoscopic and radiological response/remission in patients with Crohn's disease, in order to determine threshold levels at induction and maintenance that may be predictors of efficacy. Working hypothesis: Serum Ustekinumab levels in Crohn's disease patients are correlated with clinical, biochemical and endoscopic/radiological response/remission. Patients with an established diagnosis of Crohn's disease by usual criteria (clinical, analytical, endoscopic, radiological and/or histological) who initiate treatment with Ustekinumab (induction cohort) or who are on maintenance treatment with Ustekinumab (maintenance cohort) in a stable dosis (a minimum of 6 months) will be included.