Prevalence and clinical significance of anti-neutrophil cytoplasmic antibodies in interstitial lung disease: A retrospective cohort study

Objectives Antineutrophil cytoplasmic antibodies (ANCAs) are occasionally positive in patients with interstitial lung disease (ILD). The positivity rates of ANCAs in various types of ILD and the role of ANCAs in ILD are still unclear. The purpose of this study was to estimate the prevalence of ANCAs in Chinese people diagnosed with ILD (including idiopathic pulmonary fibrosis) and identify differences in clinical features, radiographic features, and survival between patients with ANCA-positive and ANCA-negative ILD. Methods We retrospectively reviewed the data of 706 ILD patients with available ANCA results from March 2010 to October 2023 at the First Affiliated Hospital of Ningbo University. Patient demographics, symptoms, laboratory parameters, chest CT, and pulmonary function testing results were collected and analysed at each patient’s initial diagnosis. The prevalence and associations of ANCAs with clinical characteristics and survival were evaluated. Results ANCAs were positive in 158 of the 706 (22.4%) ILD patients. Compared with ANCA-negative ILD patients, ANCA-positive ILD patients tended to be older, had higher CRP and ESR levels, and had a significantly greater proportion of rheumatoid factor positivity. In total, 58.2% (92/158) of patients were ANCA-positive on average (41.6 ± 31.4) months after ILD diagnosis. Patients with ANCA-positive ILD had higher all-cause mortality than did those with ANCA-negative ILD (33.5% vs 25.0%, p = 0.033). The usual interstitial pneumonia (UIP) pattern (56.3%) was the most common chest HRCT pattern. The proportions of patients with honeycombing (p < 0.001) and oddly shaped cysts (p < 0.001) were significantly greater in the ANCA-positive ILD group than in the ANCA-negative ILD group. Acute exacerbation (AE) of ILD (HR 2.40, 95% CI 1.37–4.22, p = 0.002) was independently associated with shorter survival, and receiving glucocorticoids combined with immunosuppressants (HR 0.30, 95% CI 0.16–0.57, p < 0.001) was independently associated with longer survival in ANCA-positive ILD patients. Conclusions The prevalence of ANCAs in patients with ILD is not rare, and ANCA testing in ILD patients is necessary. Oddly shaped cysts with or without a UIP pattern may be a characteristic chest imaging manifestation of ANCA-positive ILDs. The frequency of AEs in ANCA-positive ILD patients is high, and more attention should be given to ANCA-positive ILD patients who have AEs.