RESUMEN
A 44-year-old woman was admitted due to gross hematuria and progressive renal dysfunction. Poststreptococcal acute glomerulonephritis (PSAGN) was suspected due to her elevated anti-streptolysin O and anti-streptokinase titers and hypocomplementemia. A renal biopsy showed crescent formation and endocapillary hypercellularity with neutrophil infiltrate. An immunofluorescence analysis showed granular immunoglobulin G and C3 deposition, suggesting immune-complex-type glomerulonephritis. However, myeloperoxidase anti-neutrophil cytoplasmic antibody (ANCA) was positive, and peritubular capillaritis was observed. Furthermore, citrullinated histone H3-positive neutrophils were detected as markers for neutrophil extracellular trap formation. Therefore, she was diagnosed with ANCA-associated vasculitis superimposed on PSAGN that was the main contributor to her progressive renal injury.