Patients will be included after signing informed consent. After inclusion, patients will continue on standard dosing schedule of risankizumab (i.e. subcutaneous injections at weeks 0 and 4, then every 12 weeks (2x 75mg)). During each study visit blood will be taken in order to quantify Ctroughs and/or anti-drug antibodies towards risankizumab. In addition, Psoriasis Area and Severity Index (PASI) and Investigator's Global Assessment (IGA) score will be evaluated by a physician. Patients complete the Dermatology Life Quality Index (DLQI) and European quality of life EQ-5D instrument at each visit.
Biologics such as risankizumab are currently the most effective treatment option for patients with moderate to severe psoriasis. But they are costly for healthcare systems and still described according to a 'one dose fits all' dosing regimen, leading to potential over-and undertreatment. In this study the investigators aim to investigate the predictive value of early serum trough levels of risankizumab and determine the therapeutic window of risankizumab in psoriasis patients.