Body Mass Index and Cause-Specific Mortality After Lung Transplantation in the United States

Abstract

<h3>Purpose</h3> Both low and high body mass index (BMI) are associated with increased mortality after lung transplantation, though how extremes of BMI increase risk of death is unknown. <h3>Methods</h3> We performed a retrospective cohort study of the UNOS registry including 27,096 adults who underwent lung transplantation in the US between May 4 2005 and December 2 2020. We combined 76 reported causes of death into 16 distinct categories. We estimated cause-specific hazards for death in models adjusted for potential confounders. We evaluated effect modification by age and diagnosis. <h3>Results</h3> There was a U-shaped association between BMI at transplantation and survival after transplant attributable to greater risk of death from chronic lung allograft dysfunction (CLAD), acute respiratory failure (ARF), and primary graft dysfunction (PGD) (Table). Subjects with BMI of 24 kg/m² had the lowest risk of death from CLAD while subjects with a BMI of 18.5-28 kg/m² had lowest risk of death from ARF, with greater risk for any additional change in BMI. Every 1 kg/m² increase in BMI was associated with 4%(95% CI 1-8%) increased hazards of death from PGD. The association between BMI and death from ARF was modified by age (p= 0.004) with a strong association between high BMI and death from ARF for all ages, but between low BMI and death from ARF only among those under 65. Diagnosis modified the association between BMI and death from CLAD (p= 0.001) with stronger associations between low BMI and death from CLAD among subjects with cystic fibrosis, pulmonary hypertension and COPD, and between high BMI and death from CLAD only in COPD. <h3>Conclusion</h3> Causes of death after lung transplantation vary significantly by BMI at the time of transplantation. Further understanding of mechanisms linking BMI to death from CLAD, ARF, and PGD may identify novel targets for therapy and inform both candidate selection and post-transplant management. <h3>Table</h3> Risk of death relative to BMI of 24 kg/m² with (ARF, CLAD) or without linear splines (PGD) in cause-specific hazards models