TNF and Crohn disease: Although measuring free sTNF is challenging, due to the low detection level needed, Song et al. also previously reported measurements of free sTNF in patients with Crohn’s disease and found a similar trend, i.e. decrease of free sTNF concentrations after initiation of anti-TNF therapy [33].Total TNF concentrations were simulated and found increased after IFX administration (Fig. 2).