B39-09 Stable by Feel, Not by Flow: Disconnect Between Patient Perception and Forced Vital Capacity Change in Interstitial Lung Disease

Introduction Serial trends of pulmonary function testing values such as the forced vital capacity (FVC) remain a cornerstone for clinicians in determining disease trajectory in interstitial lung disease (ILD). While FVC has been validated as a surrogate for survival, it remains unclear how well short-term FVC changes during follow-up visits reflect patient-centered metrics such as quality of life. To investigate whether or not FVC changes correlate with patient-perceived quality of life, we asked patients across three ILD centers to guess their own FVC trajectory at their follow-up visit based on how they felt during that follow-up period. Methods Patients were enrolled at the University of Kansas, University of Florida and St. James Hospital in Dublin Ireland ILD centers. At each follow-up visit, patients were told their previous FVC percent predicted values and date of collection. Each patient was given a description of FVC and the nature of FVC changes as it relates to disease progression and then asked to guess their follow-up FVC percent predicted value. Results This study included 66 patients (14 idiopathic pulmonary fibrosis, 7 hypersensitivity pneumonitis, 15 autoimmune ILD, 11 sarcoidosis, and 19 other). The average age was 68 ± 10.1 years, with mean FVC % predicted 74 ± 20.2. The mean interval between FVC measures was 128 ± 175 days. The mean absolute difference between guessed and measured FVC % values was 7.8 percentage points. There was a strong correlation between guessed and actual FVC % (r = 0.86, p = 2E-20). However, only 37% of patients correctly predicted their trajectory (improved > +3%, stable -3 to + 3%, worsened < -3%), with most patients (55%) guessing “stable” (Figure 1). Discussion Despite a strong correlation between guessed and actual FVC % (r = 0.86), only 37% of patients accurately identified their trajectory. Most patients (55%) guessed they were “stable,” which suggested that the small magnitude of physiologic change over typical 3-month follow-up likely renders these changes imperceptible to them. These findings suggest that short-term FVC changes, while clinically meaningful, may not reflect patient-perceived health status or quality of life. The predominance of “stable” guesses underscores the importance of integrating physiologic and patient-reported measures when assessing ILD trajectory. Longer follow-up or use of sensitive tools—such as home spirometry or digital symptom tracking—may better align patient perception with objective change.