The purpose of this study is to investigate the clinical features and long-term outcome of anti-neutrophil cytoplasmic antibody (ANCA)-positive interstitial lung disease (ILD) and assess the difference between microscopic polyangiitis (MPA) associated ILD and isolated ANCA-positive idiopathic interstitial pneumonia.

ILD patients with serum ANCA-positivity were enrolled in this study.

1. Baseline data collection:

   1. Demographics information (age, gender)
   2. Clinical course
   3. Clinical symptoms and signs (cough, dyspnea, fever, fatigue, crackling, clubbing fingers, mechanics hand)
   4. Laboratory findings (blood and urine routine, liver and renal function tests, erythrocyte sedimentation rate, C reactive protein)
   5. Serologic tests (ANA , Rheumatoid factor , Anti-cyclic citrullinated peptide (CCP), Anti-dsDNA, Anti-Ro (SS-A), Anti-La (SS-B), Anti-Smith, Anti-Scl-70, Anti-Jo-1)
   6. Systemic manifestation if diagnosed as systemic vasculitis
   7. Pulmonary function tests (ventilation and diffusion capacity test)
   8. Chest high-resolution computed tomography (HRCT)

2. Treatment: treatment will be given according to the experience of each pulmonologist.

3. Follow-up:

   1. Patients were followed up at least once a year and basic laboratory tests, serologic autoantibodies, pulmonary function test and chest HRCT were evaluated routinely
   2. Follow-up end point was April 2019.

4. Outcome

Inclusion Criteria:

• Males and females
• Aged from 18 to 85 years with informed consent
• Have a diagnosis of ILD based on clinical symptoms and radiologic features, with or without histopathologic results
• Have available ANCA testing results during the first visit and follow-up period

Exclusion Criteria:

• Connective tissue disease associated ILD
• ILD induced by drug, environment, or occupational exposure
• Hypersensitivity pneumonitis and sarcoidosis

Interstitial lung disease patients with anti-neutrophil cytoplasmic antibody.

5 years

Selection bias is possible due to its retrospective nature.