P221 Autoantibodies are common in patients with idiopathic interstitial lung disease, suggesting a high prevalence of undiagnosed autoimmune connective tissue disease

Abstract Background/Aims In some patients, interstitial lung disease (ILD) may be the dominant or even sole manifestation of an otherwise unrecognised autoimmune connective tissue disease (CTD). Accurate diagnosis can be challenging given considerable overlap of the clinical, radiological and histological disease features. Distinguishing CTD related ILD (CTD-ILD) from idiopathic ILD, enables appropriate immunosuppressive treatment, informs prognosis and facilitates monitoring for other CTD associated complications. Occasionally a lung biopsy may be necessary to ensure accurate diagnosis. Autoantibodies are a hallmark feature of CTD, are highly disease specific and their presence is strongly suggestive of covert CTD-ILD. We investigated patients with idiopathic ILD for the presence of autoantibodies that may suggest misdiagnosis. Methods The serum from three subgroups of patients recruited to UK Biomarkers of Interstitial Lung Disease (BILD) were analysed: 171 with a diagnosis of idiopathic ILD and non-specific organising pneumonia on HRCT and 27 with a diagnosis of idiopathic ILD and cryptogenic organising pneumonia on HRCT. Autoantibody status was determined by radio-immunoprecipitation. Results Results are summarised in Table 1. Overall CTD-autoantibodies were identified in 15.6% of patients with idiopathic ILD, and were more common in those with NSIP, see table. Autoantibodies identified included those readily detectable e.g. anti-Jo1, in addition to rarer antibodies not included in standard assays e.g. anti-EIF3. Nearly half of all autoantibodies detected were anti-synthetase autoantibodies. Conclusion Covert-CTD is likely to be common amongst patients diagnosed with idiopathic ILD, particularly idiopathic NSIP. More specific guidance on autoantibody testing could improve diagnosis and ensure patients receive appropriate immunosuppressive treatment. Disclosure S. Tansley: None. C. Cotton: None. F.K. McMorrow: None. H. Lu: None. R.P. New: None. L.G. Spencer: None. N.J. McHugh: None. R.G. Cooper: None.