Beyond Heart Failure: A Case of Missed Anti-neutrophil Cytoplasmic Antibody (ANCA)-Associated Glomerulonephritis.

Anti-neutrophil cytoplasmic antibody-associated vasculitis, abbreviated as ANCA-associated vasculitis or AAV, presenting as pauci‑immune glomerulonephritis may be misdiagnosed in elderly individuals with comorbid cardiovascular disease. We present a case of a 75-year-old female with type 2 diabetes mellitus, hypertension, atrial fibrillation and presumed heart failure with preserved ejection fraction (HFpEF) who developed progressive renal decline misattributed to diuretics and cardio-renal syndrome over eight months. Workup revealed myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA) positivity and renal biopsy confirmed pauci-immune focal proliferative glomerulonephritis. Induction therapy with high‑dose glucocorticoids and oral cyclophosphamide failed to avert dialysis dependency. This case reflects that the interpretation of N-terminal pro-B-type natriuretic peptide (NT-pro BNP) in chronic kidney disease (CKD) is limited and overlapping symptoms complicate diagnosis. Current clinical guidelines recommend early ANCA testing, biopsy‑confirmed diagnosis, and induction therapy combining glucocorticoids with either rituximab or cyclophosphamide, with or without avacopan; plasma exchange may be considered for rapidly progressive glomerulonephritis. This case underscores the importance of early nephrology referral, ANCA serological screening, and prompt renal biopsy to avert irreversible renal injury despite guideline‑adherent therapy.