Renal Involvement and Early Relapse Patterns in Granulomatosis with Polyangiitis: A Prospective Cohort from a Tertiary Care Center

Abstract Renal involvement is a major determinant of prognosis in granulomatosis with polyangiitis (GPA), yet population-specific data from the Middle East remain scarce. In this prospective cohort study, 186 consecutive patients diagnosed with GPA between 2013 and 2021 at a tertiary referral center were followed to evaluate the clinical characteristics, relapse patterns, and prognostic factors associated with renal involvement, with particular emphasis on urinary findings and ANCA specificity. Renal involvement was present in 44% of patients and was associated with older age, male predominance, higher baseline disease activity, and greater MPO-ANCA positivity. Despite more intensive induction therapy, renal involvement alone did not independently predict higher relapse frequency or mortality after adjusting for baseline severity and treatment. Within the renal cohort, gross hematuria emerged as the strongest predictor of relapse (odds ratio [OR] 7.1, 95% confidence interval [CI] 1.7–20.4), followed by proteinuria (OR 2.5, 95% CI 1.06–6.6). PR3-positive renal patients had a markedly higher rate of early relapse within six months than MPO-positive patients (41% vs 11%, P = 0.02), whereas MPO-positive patients more often achieved drug-free remission (77% vs 49%, P = 0.03). Renal involvement signified greater initial disease severity but did not independently worsen long-term outcomes under standardized therapy. These findings support integrating urinary markers and ANCA subtype into individualized risk stratification and follow-up strategies for patients with GPA.