Association of Monocyte Count With Lung Function and Exercise Capacity Among Hospitalized COVID-19 Survivors: A 2-Year Cohort Study

Abstract

Background: Abnormal changes of monocytes have been observed in acute COVID-19, whereas associations of monocyte count with long COVID were not sufficiently elucidated. Methods: A cohort study was conducted among COVID-19 survivors discharged from hospital. The primary outcomes were core symptoms of long COVID, distance walked in 6 min, and lung function, and the secondary outcomes were health-related quality of life and healthcare use after discharge. Latent variable mixture modeling was used to classify individuals into groups with similar trajectory of monocyte count from discharge to 2-year after symptom onset. Multivariable adjusted generalized linear regression models and logistic regression models were used to estimate the associations of monocyte count trajectories and monocyte count at discharge with outcomes. Results: In total, 1389 study participants were included in this study. Two monocyte count trajectories including high to normal high and normal trajectory were identified. After multivariable adjustment, participants in high to normal high trajectory group had an odds ratio (OR) of 2.52 (95% CI, 1.44–4.42) for smell disorder, 2.27 (1.27–4.04) for 6-min walking distance less than lower limit of normal range, 2.45 (1.08–5.57) for total lung capacity (TLC) < 80% of predicted, 3.37 (1.16–9.76) for personal care problem, and 1.70 (1.12–2.58) for rehospitalization after discharge at 2-year follow-up compared with those in normal trajectory group. Monocyte count at discharge showed similar results, which was associated with smell disorder, TLC < 80% of predicted, diffusion impairment, and rehospitalization. Conclusions: Monocyte count may serve as an easily accessible marker for long-term management of people recovering from COVID-19.