We would like to thank Vande Casteele and coworkers for their interest in our systematic review.[1, 2] Although antibodies against tumour necrosis factor α (anti-TNFα) drugs induce and maintain remission in inflammatory bowel diseases, approximately 30% of patients do not respond to these medications, and up to 40% of responders need multiple dose adjustments to maintain remission in the long term.[3-7]
Monitoring the treatment based on anti-TNFα and antibodies to the drug serum levels seems to be a promising tool to optimise therapy with these medications. However, several questions about this strategy remain unanswered.[2, 8] First, current methods suffer from several limitations and a definitively accurate technique has not been developed yet. Second, a high inter-individual variability has been described; therefore, the threshold for therapeutic concentration cannot be precisely established.[2, 8] Finally, the value of individualised treatment based on drug levels monitoring has not been proven in clinical practice.
Vande Casteele et al. propose a new method for measuring anti-TNFα drug levels in a dry blood spot obtained via capillary puncture. This test seems very attractive for its use in clinical practice, with the advantages of avoiding venous puncture, on one hand, and providing the results immediately, on the other. However, it seems to have some limitations. Of note, the concentration of the antibodies against the drug, which is essential for decision making in patients under anti-TNFα treatment, could not be measured with this test.[2, 8] Furthermore, as the authors recognise, the accuracy of this new test needs to be validated.
In conclusion, the best method for measuring anti-TNFα and antibody levels remains to be established, and the impact of monitoring anti-TNFα therapies based on serum levels needs to be proven. The development of new tests to make this measurement more feasible will facilitate the implementation of this strategy in the clinical management of patients receiving anti-TNFα therapies.