In summary, our observational study suggests that physicians should continue to measure and consider ESR, CRP, Hb and leukocyte count when assessing disease activity and more systematic and integrated use of these routine as well as new (S100A12) laboratory markers, together with clinical tools (PVAS, PGA) can assist and improve therapeutic decision making in the pediatric populations across vasculitis subtypes but most profoundly for subtypes such as GPA that are associated with PR3-ANCA. Here, CRP is linked to granulomatosis with polyangiitis.