The relationship between GAP stage and quality of life in IPF and systemic sclerosis-related ILD is diagnosis-dependent

Background: The Gender-Age-Physiology (GAP) model predicts mortality in idiopathic pulmonary fibrosis (IPF) and systemic sclerosis-related interstitial lung disease (SSc-ILD). Whether GAP stage is associated with health-related quality of life (HRQL) in these diseases is unknown. Objective: To determine the relationship between GAP stage and HRQL in IPF and SSc-ILD. Methods: HRQL was assessed using the Kings Brief Interstitial Lung Disease (K-BILD) questionnaire, scored 0-100 with higher scores indicating better HRQL. GAP stage was calculated based on gender, age, FVC and DLCO, with stages 1-3 indicating successively poorer prognosis. ANCOVA was used to compare K-BILD scores across GAP stages, adjusting for diagnosis and diagnosis-by-GAP interaction. Results: Among 58 patients with IPF, 23 (40%) were in GAP stage 1, 28 (48%) in GAP stage 2, and seven (12%) in GAP stage 3. Among 27 patients with SSc-ILD, 22 (81%) and 5 (19%) were in GAP stages 1 and 2, respectively, and none were in GAP stage 3. Mean (95% CI) K-BILD scores are shown in the table. Higher GAP stage was associated with worse K-BILD score independent of ILD diagnosis (p Table: mean (95% CI) K-BILD total scores: Conclusions: A given difference in GAP stage was associated with a greater difference in HRQL among SSc-ILD patients than among IPF patients, suggesting that lung disease severity has an especially large impact on HRQL in SSc-ILD.