Clinical predictors for IPF in an unclassified patient population with indication to transbronchial cryobiopsy

<bold>Introduction:</bold> In patients with ILD without definite or probable UIP pattern on CT, invasive diagnostic procedures should be considered for further evaluation. In the present analysis, clinical predictors for the presence of IPF in this clinical setting were investigated. <bold>Methods:</bold> The analysis included patients with previously unclassified ILD presenting for evaluation at our tertiary ILD center between November 2017 and December 2021, and for whom the indication for histological confirmation was made in a multidisciplinary discussion. <bold>Results:</bold> 402 patients, 38% female, 68±12 years old, received cTBB and were analysed retrospectively. In 18 patients an additional surgical lung biopsy was needed. A definitive ILD diagnosis was achieved in >90% of cases. After MDD, IPF was diagnosed in 66 cases. IPF patients were older than patients with other ILD, significantly more likely to report occupational exposure and less likely to report domestic exposure. CT showed more frequent UIP features, such as honeycombing, less frequent NSIP features, e.g. ground-glass infiltrates. IPF patients were less likely to show lymphocytosis in BAL, histology showed more frequent UIP features and less frequent evidence of other ILD. In the multivariate analyses, radiological UIP features, BAL lymphocytosis, absence of domestic exposures and histology that was not suggestive of other ILD were independent predictors of IPF diagnosis, but gender, BMI, age and histological UIP pattern were not. <bold>Conclusion:</bold> Clinical parameters, including BAL, may contribute to the diagnosis of IPF in some cases. In the absence of evidence of other ILD, the exact significance of histology must be critically reviewed.