The invention refers to a method for diagnosing an individual who is to be subjected to or is being subjected to an anti-tumor necrosis factor alpha (TNFα or TNF) treatment to asses the responsiveness to an anti-TNF treatment which comprises the detection of immunoglobulin(s) against one or more biomarker proteins in a bodily fluid or an excrement of said patient, and sorting the individual into one of two categories based on detection of said immunoglobulin(s), wherein individuals are classified as NON-responder or responder. The invention refers to diagnostic kits comprising said one or more biomarker proteins and the use of these kits for assessing the responsiveness to an anti-TNF treatment of an individual who is to be subjected to or is being subjected to an anti-TNFα treatment.
