Predictors of Impaired Diffusing Capacity of Lung for Carbon Monoxide in Post-COVID-19 Pulmonary Fibrosis Patients

Abstract

Background & objective: While Acute Respiratory Distress Syndrome (ARDS) is a hallmark of severe COVID-19, survivors often face long-term sequelae, most notably post-COVID-19 Pulmonary Fibrosis (PCPF). The Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) is a sensitive physiological marker for alveolar-capillary integrity. This study aimed to determine the prevalence and predictors of impaired DLCO among patients with radiologically confirmed PCPF in Bangladesh. Methods: This cross-sectional analytical study was conducted at the Diffuse Parenchymal Lung Disease (DPLD) Clinic, Dhaka Medical College Hospital, from September 2021 to August 2022. Forty-eight patients with PCPF were enrolled. Pulmonary Function Tests (PFTs), including spirometry and DLCO (single-breath technique), were performed at least 12 weeks after acute infection. Patients were categorized into Cases (impaired DLCO < 75% predicted) and Controls (normal DLCO = 75%). Statistical analysis was performed using SPSS, with level of significance set at p < 0.05. Results: The prevalence of impaired DLCO was 27.1% (n=13) in the study cohort. Patients with impaired DLCO were significantly older (62.5 ± 3.4 vs. 53.6 ± 7.9 years; p < 0.001) and more likely to be female (61.5% vs. 28.6%; p = 0.040). A history of chronic obstructive pulmonary disease (COPD) was a strong predictor of impairment (OR = 9.6; 95% CI: 2.2–41.5; p = 0.004). Biochemical markers, including serum creatinine (p = 0.003), D-dimer (p < 0.01), and C-Reactive protein (p = 0.008), were significantly elevated in the impaired group. Furthermore, patients with a history of severe acute COVID-19 illness were 13.5 times more likely to exhibit diminished DLCO (95% CI: 2.9–61.2; p = 0.001). Conclusion: Diminished diffusing capacity of the lung for carbon monoxide is prevalent among PCPF survivors and is strongly associated with advanced age, female gender, pre-existing COPD, and the severity of the initial infection. These findings underscore the importance of routine DLCO monitoring in the post-COVID-19 clinical pathway to facilitate early intervention and improve long-term respiratory outcomes.

Ibrahim Card Med J 2025; 15 (2): 09-15