CO10 - Integrating DLCO with FVC in Fibrotic Hypersensitivity Pneumonitis: How do we better model mortality in Progressive Pulmonary Fibrosis ?
James Tadjkarimi (UK)1; Evelyn Lynn (UK)1; Punchalee Kaenmuang (Thailand)2; Athina Trachalaki (UK)1; Vasileios Kouranos (UK)1; Peter George (UK)1; Simon Bax (UK)1; Maria Kokosi (UK)1; Carmel Stock (UK)1; Richard Hewitt (UK)1; Elizabeth Renzoni (UK)1; Athol Wells (UK)1;
1 - Interstitial Lung Disease Unit, Royal Brompton Hospital, London; 2 - Respiratory and Respiratory Critical Care Unit, Division of Internal Medicine, Faculty of Medicine, Prince of Songkla University - Hat Yai;
Keywords: Fibrotic Hypersensitivity Pneumonitis; Prognostication; Real-world cohort;
Select the theme: Progressive Pulmonary Fibrosis
Type: Original Papers
Presentation: Oral Communication

Introduction: Current Progressive Pulmonary Fibrosis (PPF) guidelines define physiological progression using either absolute decline in forced vital capacity (FVC) by >5% or >10% diffusing capacity for carbon monoxide (DLco) within one year. Interpreting either in isolation risks not capturing the full spectrum of disease behaviour. 

Objectives: We examined whether integrating DLco decline into FVC trajectory better delineates individuals with PPF at increased risk of death. 

Materials and Methods: In a real-world cohort of 416 patients with fibrotic hypersensitivity pneumonitis (fHP) we assessed longitudinal pulmonary function and mortality data. Patients were initially stratified at first follow-up lung function by FVC decline of >10% decline, 5-10% decline, or stable (<5% decline). In patients with 5-10% decline or stable FVC, additional DLco strata were applied to assess whether combined physiological decline improved prognostic separation. Survival was compared across groups using log-rank testing. 

Results: Using FVC alone, 95/416 patients (22.8%) had >10% FVC decline, 49/416 (11.8%) had 5–10% decline, and 272/416 (65.4%) had <5% decline; these groups showed significant differences in mortality (p<0.0005)[ figure 1.] Among patients with 5–10% FVC decline, those with concomitant DLco decline >10% showed worse survival than those without, although this did not reach significance (19 vs 30 patients; p=0.06). Among patients with <5% FVC decline, DLco decline >15% identified a subgroup with significantly worse mortality (19 vs 253 patients; p=0.04). Excluding those with definite >10% FVC decline, DLco identified 38/321 patients (11.8%) with an adverse prognosis despite the absence of definite FVC decline (p<0.0005). In the full cohort, an integrated FVC and DLco model reclassified 133/416 patients (32%) as decline and 283/416 (68.0%) as stable. These groups showed marked mortality separation (p<0.0005) [Figure 2.] 

Conclusions: In fHP, FVC alone may underestimate clinically meaningful progression. Integrating DLco decline with FVC improves mortality stratification, particularly in patients with borderline or apparently stable FVC. Using an integrated physiological score anchored to survival may provide a more sensitive physiological definition of progression and should be considered in future PPF guidelines.

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