Background: The existence of antineutrophil cytoplasmic antibody (ANCA)-positive pulmonary fibrosis (PF) has recently been recognized. Objectives: The aim of this study was to clarify whether there is any difference in the clinical features between ANCA-positive PF and ANCA-negative PF. Methods: A retrospective study was carried out on 53 patients with idiopathic PF whose myeloperoxidase (MPO)- and proteinase 3 (PR3)-ANCA levels were measured. After dividing the patients into ANCA-positive and ANCA-negative PF, we compared their symptoms, pulmonary function tests, chest CT findings, bronchoalveolar lavage findings, the effects of therapy and survival rates. Results: 17 of the 53 patients with idiopathic PF were MPO-ANCA-positive, 2 were PR3-ANCA-positive and 34 were negative for both ANCA types. Lactate dehydrogenase was lower in ANCA-positive PF than in ANCA-negative PF. However, there was no significant difference in the symptoms, lung function tests, CT findings and bronchoalveolar lavage findings. Corticosteroid therapy tended to be more effective in ANCA-positive PF, but the overall survival rate in ANCA-positive PF was not different from that in ANCA-negative PF. However, the low-titer (<50 EU) group showed better survival than the high-titer (≥50 EU) group in ANCA-positive PF. ANCA titers of the patients who developed microscopic polyangiitis were higher than of those who did not develop it in ANCA-positive PF. Conclusions: Our studies showed little difference in the clinical features between ANCA-positive and ANCA-negative PF. However, it may be important to measure ANCA when idiopathic PF is diagnosed, because a high titer of ANCA suggests a poor prognosis and the association with microscopic polyangiitis.

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