B69-01 Body Mass Index as a Predictor of Lung Function at Pulmonary Tuberculosis Diagnosis

Abstract Rationale Post-tuberculosis lung disease (PTLD) has been increasingly recognized as a significant global health challenge, with nearly half of tuberculosis (TB) survivors having impaired lung function despite microbiologic cure. Previous studies have identified an association between undernutrition, defined as a low body mass index (BMI), and increased severity of disease on chest X-ray at TB diagnosis. However, the relationship between BMI and lung function has not been well-established. This study aimed to assess whether low BMI was associated with worse lung function at the time of pulmonary TB diagnosis. Methods For an ongoing prospective cohort study in Johannesburg, South Africa, adults with and without HIV were enrolled within two weeks of treatment initiation for newly diagnosed, drug-susceptible pulmonary TB. Baseline demographic and clinical data were obtained at enrollment, and spirometry was performed according to ATS/ERS standards. The World Health Organization classification for low BMI was used to define the cutoff of 18.5 kg/m². Forced expiratory volume in one second (FEV1) z-scores were used as a measure of lung function. Crude and adjusted linear regression models were used to assess the relationship between BMI and FEV1 z-scores at time of diagnosis. Results Among 249 participants enrolled in the study, 96 (39%) had a low BMI. Those with low BMI were more likely to be male (84% vs. 58%, p 0.001), have a history of smoking (76% vs. 44%, p 0.001), and have more radiographic disease (median chest X-ray Timika score 72 IQR:55-85 vs. 51 13-70, p 0.001; median chest CT score 15 IQR:12-19 vs. 12 8-16, p 0.001). At TB diagnosis, participants with low BMI had significantly lower median FEV1 z-scores (-2.01 IQR:-2.80,-0.95) compared to those with BMI ≥18.5 (-1.08 IQR:-2.17,-0.11, p 0.001). In both unadjusted and adjusted models, lower BMI was associated with lower FEV1 z-score, with a β of 0.099 (p 0.001) after adjustment for age, sex, HIV status, and smoking. Conclusions Within this cohort study, BMI was significantly associated with FEV1 z-score in participants with TB, increasing the body of literature suggesting undernutrition may contribute to TB-associated lung function impairment. Future analyses will aim to assess the longitudinal relationship between BMI trajectories throughout treatment and lung function following microbiologic cure. This abstract is funded by: R01AI166988