TNF and rheumatoid arthritis: Long disease duration and high disease activity (DAS28 5.76 ± 1.35 in RA patients, ASDAS 15.41 ± 6.13 in axial SpA) before treatment with TNFα blockers can be the factors also responsible for the fact that we did not find correlation between detectable levels of TNFα blockers and anti-drug Abs with clinical efficacy.