TNF and rheumatoid arthritis: Therapeutic drug monitoring using measurement of serum drug levels (a proxy for tissue levels) and/or ADAs thus holds potential to optimize management, and a strong correlation between TNF inhibitor serum trough levels, ADAs, and treatment response has been described in IBD, RA, and psoriasis (Baert et al., 2003, Chen et al., 2015, Lecluse et al., 2010).