Challenges of defining renal response in ANCA-associated vasculitis: call to action?

Lay Summary This review focuses on kidney survival of patients with anti-neutrophil cytoplasmic antibody-associated vasculitis. Impaired kidney function is a major contributor to morbidity and mortality. In this review we discuss current knowledge about recovery potential of the kidney, influences thereof and how future modern approaches may help to improve prediction. This will eventually include kidney biopsies, markers measured in blood and urine and baseline characteristics of patients. Avoiding end-stage kidney disease in patients with anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) has a high therapeutic priority. Although renal response is a crucial measure to capture clinically relevant changes, clinal trials have used various definitions and no well-studied key surrogate markers to predict renal outcome in AAV exist. Differences in clinical features and histopathologic and therapeutic approaches will influence the course of kidney function. Its assessment through traditional surrogates (i.e. serum creatinine, glomerular filtration rate, proteinuria, hematuria and disease activity scores) has limitations. Refinement of these markers and the incorporation of novel approaches such as the assessment of histopathological changes using cutting-edge molecular and machine learning mechanisms or new biomarkers could significantly improve prognostication. The timing is favourable since large datasets of trials conducted in AAV are available and provide a valuable resource to establish renal surrogate markers and, likely, aim to investigate optimized and tailored treatment approaches according to a renal response score. In this review we discuss important points missed in the assessment of kidney function in patients with AAV and point towards the importance of defining renal response and clinically important short- and long-term predictors of renal outcome.Funding Agencies|Austrian Science Fund [J 4664-B]; Wellcome Trust; Health Research Board [203930/B/16/Z]; Health Service Executive, National Doctors Training and Planning; Health and Social Care, Research and Development Division, Northern Ireland