Introduction: A majority of IPF patients in Sweden are treated with antifibrotic drugs, but not all. The reasons for not treating patients varies but are based on individual decisions by the treating physician together with the patient. In what way untreated patients differ from treated and if there are characteristics at the time of diagnosis that affects the initiation of treatment is less known.

Aim: To explore differences between IPF-patients initiating and not initiating antifibrotic treatment.

Methods: Data from the Swedish IPF-registry was extracted, including patients diagnosed between 2014 ? 2022. Baseline was considered as the date of diagnosis. Patients were considered treated with antifibrotic drugs (pirfenidone or nintedanib) if it was initiated within 90 days from diagnosis. Non-treated patients were defined as patients not initiating treatment within 24 months after diagnosis. Patient characteristics were described at baseline and compared between untreated and treated patients.

Results: Five hundred and thirty-two patients were included of which 371 started treatment and 161 did not. Treated patients were younger (median age: 72 vs 74 (p= 0.022)), had worse lung function (FVC % predicted, median 69 vs 82, (p < 0.001); DLCO % 47 vs 56, (p < 0.001); TLC % 64 vs 72, (p < 0.001)) and were more often treated with oxygen (5% vs 1% (p = 0.011) compared to non-treated patients.

Conclusion: Our real-world data indicate that patients receiving antifibrotics differ compared to those not receiving treatment, suggesting that antifibrotics is mainly prescribed to patients with more advanced disease.