Monocyte count and the risk for acute exacerbation of fibrosing interstitial lung disease: A retrospective cohort study

Recent studies have suggested that an increased peripheral monocyte count predicts a poor outcome in fibrosing interstitial lung disease (ILD). However, the association between an increased monocyte count and acute exacerbations (AEs) of fibrosing ILD remains to be elucidated. Our retrospective cohort study aimed to assess the impact of peripheral monocyte count on AEs of fibrosing ILD. We analyzed the electronic medical records of 122 consecutive patients with fibrosing ILD and no prior history of an AE, who were treated with anti-fibrotic agents from August 2015 to December 2018. We determined their peripheral monocyte counts at anti-fibrotic agent initiation and performed univariate and multivariate Cox regression analyses of time-to-first AE after anti-fibrotic agent initiation to assess the impact of monocyte count on AEs of fibrosing ILD. Twenty-six patients developed an AE during the follow-up period, and there was an increased monocyte count at anti-fibrotic agent initiation in these patients compared to those who did not develop an AE. There was also a significantly shorter time-to-first AE of fibrosing ILD in patients with a higher absolute monocyte count. Subgroup analyses indicated similar results regardless of the idiopathic pulmonary fibrosis diagnoses. This association was independently significant after adjusting for the severity of the fibrosing ILD. Using our results, we developed a simple scoring system consisting of two factors—monocyte count (<>380 µL⁻¹) and ILD-gender, age, physiology score (<>4 points). Our findings suggest that the absolute monocyte count is an independent significant risk factor for AE in patients with fibrosing ILD. Our simple scoring system may be a predictor for AEs of fibrosing ILD, although further studies are needed to verify our findings.