Can BMI and Weight Loss Predict Mortality in Fibrotic Interstitial Lung Disease?

In patients with fibrotic interstitial lung disease (ILD), both low body mass index (BMI) and weight loss are associated with increased 1-year mortality rates, according to study results recently published in the journal CHEST.

An observational, retrospective, multicenter cohort study was conducted among patients from 2 large prospective cohorts: the 6-center Canadian Registry for Pulmonary Fibrosis (CARE-PF, derivation cohort) and the ILD registry at the University of California, San Francisco (UCSF, validation cohort). The researchers investigated whether BMI and weight loss are predictive of mortality among patients with common fibrotic ILD subtypes, with adjustments made for established risk prediction models. Pulmonary function tests (PFTs) were performed when clinically indicated. Patients’ height and weight, which were recorded at the time of each PFT measurement, were used to calculate an individual’s BMI. In the current study, patients were subcategorized as underweight (BMI <18.5 kg/m²), normal weight (BMI, 18.5 to 24.9 kg/m²), overweight (BMI, 25 to 29.9 kg/m²), and obese (BMI >30 kg/m²).

A total of 1786 patients were enrolled in the CARE-PF derivation cohort and 1779 patients in the UCSF validation cohort. When the 2 cohorts were combined, the most common diagnoses were idiopathic pulmonary fibrosis in 34% of participants, connective tissue disease-associated ILD in 32%, unclassifiable ILD in 20%, and fibrotic hypersensitivity pneumonitis in 14%.

Results of the study showed that based on the analysis adjusted for GAP (gender, age, physiology) Index, compared with participants with normal BMI, mortality rates were highest in  those who were underweight (hazard ratio [HR], 3.19; 95% CI, 1.88-5.43; P <.001) and were lowest in patients who were overweight (HR, 0.52; 95% CI, 0.36-0.75; P <.001) or were obese (HR, 0.55; 95% CI, 0.37-0.83; P <.001).

Among those participants who experienced a weight loss of 2 kg or more within 1 year, an increased risk for death in the subsequent year was reported (HR, 1.41; 95% CI, 1.01-1.97; P =.04), following adjustment for baseline BMI category and ILD-GAP Index. A plateau in the mortality risk was seen among patients with greater weight loss. Consistent findings were reported among those in the validation cohort.

The researchers concluded that these results provide additional data for use by clinicians to refine prognostic estimates, along with other validated physiologic and demographic parameters. Future studies are warranted to better characterize the link between low BMI and weight loss in patients with fibrotic ILD, and to establish the possible use of interventions designed to target BMI.

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures. 

Reference 

Comes A, Wong AW, Fisher JH, et al. Association of body mass index and change in weight with mortality in patients with fibrotic interstitial lung disease.  CHEST. Published online November 14, 2021. doi:10.1016/j.chest.2021.11.008