Monitoring ustekinumab (UST) concentrations and antibodies-to ustekinumab (ATU) during IBD treatment may allow more informed decisions in assessing exposure/response and appropriate dosing. To aid in interpreting results in the context of Janssen’s published UST results, the reliability of different assays measuring UST and ATU were compared with those from Janssen. This abstract reports the comparison of the UST and ATU assays from Laboratory Corporation of America (LabCorp, Calabasas, CA, USA) and Janssen (JRD, Spring House, PA, USA).