Anemia as a risk factor for disease progression in patients admitted for COVID-19: data from a large, multicenter cohort study

In respiratory infections, anemia is both a consequence of acute inflammation and a predictor of poor clinical outcomes. There are few studies investigating the role of anemia in COVID-19, suggesting a potential role in predicting disease severity. In this study, we aimed to assess the association between the presence of anemia at admission and incidence of severe disease and death in patients hospitalized for COVID-19. Data from all adult patients admitted for COVID-19 in University Hospital “P. Giaccone” Palermo, and University Hospital of Bari, Italy, were retrospectively collected from 1st of September 2020 to 31 August 2022. The association between anemia (defined as Hb < 13 g/dl and < 12 g/dl in males and females, respectively), in-hospital mortality and severe COVID-19 was tested using a Cox’s regression analysis. Severe COVID-19 forms were defined as admission to intensive or sub-intensive care unit or a qSOFAscore ≥ 2 or CURB65scores ≥ 3. p values were calculated using the Student’s t test for continuous variables and the Mantel–Haenszel Chi-square test for categorical ones. The association between anemia and the mortality was made using a Cox’s regression analysis, adjusted, in two models, for the potential confounders and using a propensity score. Among the 1562 patients included in the analysis, prevalence of anemia was 45.1% (95% CI 43–48%). Patients with anemia were significantly older (p < 0.0001), reported more co-morbidities, and presented higher baseline levels of procalcitonin, CRP, ferritin and IL-6. Overall, the crude incidence of mortality was about four times higher in patients with anemia compared to those without. After adjusting for 17 potential confounders, the presence of anemia significantly increased the risk of death (HR = 2.68; 95% CI: 1.59–4.52) and of risk of severe COVID-19 (OR = 2.31; 95% CI: 1.65–3.24). The propensity score analysis substantially confirmed these analyses. Our study provides evidence that, in patients hospitalized for COVID-19, anemia is both associated with a more pronounced baseline pro-inflammatory profile and higher incidence of in-hospital mortality and severe disease.