Background: Diagnosing patients with anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) can be challenging due to its rarity, complexity and wide variety of symptoms. Diagnostic delay may lead to delayed treatment potentially leading to progressive disease and chronic damage. Few studies have addressed real-life diagnostic pathways to identify opportunities to improve the diagnostic phase for AAV patients. Therefore, we evaluated the diagnostic phase of AAV patients in the Netherlands. Methods: This study is a retrospective, observational study of electronic medical records data in hospitals focusing on diagnostic procedures during the first assessment until diagnosis. Results: 230 AAV patients in 9 Dutch hospitals diagnosed with mainly granulomatosis with polyangiitis (73%) and generalized disease (72%) with major organ involvement (kidney, heart, lungs and nervous system) were included. First assessments upon hospital presentation was performed by a specialist in internal medicine ...