Liu, E

Abstract Background Single breath diffusing capacity of the lung for carbon monoxide (DLCO) remains the most widely used test to assess pulmonary gas exchange. GLI DLCO reference equations are based on a larger, more diverse dataset and offer age-specific and internally consistent reference values. However, their impact on interpretation in a real-world population remains uncertain. Research Question Describe the direction and magnitude of DLCO interpretation changes resulting from our multicenter PFT laboratory transition from Miller to GLI reference equations. Study Design and Methods In this multicenter cross-sectional study, we reanalyzed 88,060 DLCO measurements in a large pulmonary function laboratory database performed between 2016 and 2022 using GLI and Miller reference equations, stratified by self-reported race and ethnicity. Baseline patient characteristics and lung function measurements were summarized with continuous characteristics as median (IQR) and categorical variables as n (%). Kruskal-Wallis test was used to evaluate the difference between GLI and Miller DLCO % predicted difference between races, and two-by-two and four-by-four tables were generated to summarize the proportion of concordance and discordance of GLI to Miller severity levels. A repeated measures multivariable logistic regression was used to evaluate discordance between GLI and Miller severity and patient characteristics (age, sex, race, and BMI). Results We included 63,357 individuals with 88,060 PFT visits; 91.6% (58,076) identified as Caucasian, 5.2% (3,262) as Black, 1.4 % (895) as Asian, and 1.8% (1,113) as mixed/other race. Fifty-one percent were female with an median age of 64 years (range: 5- 85). 7.4% (6509) of DLCO results were discordant, with 0.5% (n = 439) abnormal by GLI only, and 6.9% (n = 6070) abnormal by Miller only. Compared to the Miller, GLI interpretations were associated with a greater shift toward normal interpretations. Younger age, lower BMI, female sex, and being of NE Asian, SE Asian, or Other/mixed race compared to Caucasian were associated with higher odds of discordance in DLCO severity/normal classification. Interpretation The use of GLI reference equations substantially alters the interpretation of DLCO results, shifting a meaningful subset of patients from abnormal to normal classification. While GLI reference equations offer more comprehensive, population-based approach, it is crucial to place these interpretations within the context of the patient presentation until further investigations more clearly define the clinical implications of these transitions. This abstract is funded by: none

Abstract Rationale Inflammatory bowel disease (IBD) is increasingly recognized as a systemic disorder, with extraintestinal manifestations (EIMs) involving multiple organ systems. Pulmonary involvement, particularly interstitial lung disease (ILD), remains an underrecognized manifestation of IBD. Its prevalence, clinical characteristics, and risk factors in IBD remain poorly defined. Methods We conducted a retrospective study of adults (≥18 years) with IBD who had at least one encounter in our health system between January 1, 2013 and December 31, 2023. IBD, and ILD cases were identified using ICD-9/ICD-10 codes, with ILD diagnoses confirmed by thoracic radiologists. Demographic, clinical, pulmonary, smoking, medication, and surgical data were abstracted. Associations between patient characteristics and ILD were evaluated using both a cohort design and a matched case-control design (1:3 ratio). Mortality was assessed using a Cox proportional hazards model with ILD as a time-dependent covariate. Results Among 875 patients with IBD, 109 (12%) had ILD. Radiographic patterns included nonspecific interstitial pneumonia (NSIP, 27%), indeterminate (26%), definite/probable UIP (24%), hypersensitivity pneumonitis (15%), and organizing pneumonia (8%). Pulmonary function testing demonstrated predominantly restrictive physiology and impaired diffusion capacity. In multivariable analysis, higher BMI (OR 1.04), bronchiectasis (OR 2.65), ex-smoking (OR 2.15), and use of adalimumab (OR 2.04) or infliximab (OR 2.14) were independently associated with ILD. The matched case-control design confirmed these findings and also identified older age (OR 1.04) as a significant factor. ILD was strongly associated with mortality (HR, 3.78; 95% CI, 2.50-5.72; p < 0.001). Conclusions ILD occurs in a meaningful subset of patients with IBD and is associated with older age, higher BMI, prior smoking, bronchiectasis, and TNF inhibitor use. ILD confers a markedly increased risk of death, highlighting the importance of early recognition and close monitoring in this population. This abstract is funded by: None