C41-03 When Tissue Still Leaves Issues: The Importance of Early Serological Testing in Patients With Suspected ANCA Vasculitis

Abstract Introduction The differential diagnosis for pulmonary nodules is broad and includes infection, malignancy, and autoimmune diseases. Because of the overlapping features among these entities, establishing an accurate diagnosis can be challenging without histopathologic confirmation. However, biopsy findings demonstrating necrotizing granulomas are often nonspecific and can further delay diagnosis and treatment. When histopathologic results are non-diagnostic, timely and disease-specific serologic evaluation is critical to guide appropriate therapy and prevent irreversible organ damage. Here, we present a case of granulomatosis with polyangiitis (GPA) that highlights the importance of an early and comprehensive serologic workup and how cognitive errors, such as anchor bias, can negatively affect patient outcomes. Case Report A 69-year-old female presented to the ED for left-sided pleuritic chest pain. A chest CT revealed a right lower lobe masslike consolidation, bilateral pulmonary nodules, and lymphadenopathy concerning for malignancy. She was therefore admitted to the hospital, and a CT-guided lung biopsy was performed. While awaiting the pathology results, the patient developed mild hemoptysis, worsening acute kidney injury (AKI), and hypotension requiring ICU care for vasopressor support, broad spectrum antibiotics, and continuous renal replacement therapy (CRRT). Pathology from the lung biopsy demonstrated necrotizing granulomas, prompting an expanded diagnostic work-up. Serological testing demonstrated a negative ANCA (1:20), positive PR3 IgG (73), negative MPO (0), and positive ANA (1:1280, centromere pattern). Infectious studies, including tuberculosis and endemic fungal serologies, were negative. Due to her lack of renal recovery, a kidney biopsy was obtained showing crescentic glomerulonephropathy with 60% interstitial fibrosis and tubular atrophy, findings consistent with GPA. Although she was successfully weaned off vasopressors, she remained dialysis dependent with a poor likelihood of renal recovery due to the delay in diagnosis. Given her poor renal prognosis and the risk of infection, a risk/benefit conversation with the patient led to deferring immunosuppression. Discussion This case illustrates the diagnostic complexity of pulmonary necrotizing granulomas, where infection and malignancy are often initially favored over autoimmune etiologies, and anchor bias can lead to delays in diagnosis. In such cases, early serological evaluation for autoimmune etiologies is essential to prevent delays in initiating immunosuppressive therapy and preventing progression to end stage renal disease. Our case highlights the importance of including both ANCA and PR-3/MPO antibody testing when evaluating for ANCA vasculitis, as the PR3 antibody demonstrates substantially higher sensitivity compared to ANCA antibody testing alone (73% vs 11%). Early, sensitive serologic evaluation is warranted to prevent misdiagnosis. This abstract is funded by: None