Although rib fractures are a risk factor, not all rib fracture patients will develop delayed hemothorax. This study aimed to evaluate risk factors which can identify rib fracture patients in the emergency department who may develop delayed hemothorax.

Adult patients seen in the emergency room between January 2016 and February 2021 with rib fractures caused by blunt chest trauma were included in this retrospective observational study. Patients who underwent chest tube insertion within 2 days and those without follow-up chest radiographs within 2–30 days were excluded. We used a stepwise backward-elimination multivariable logistic regression model for analysis.

A total of 202 patients were included in this study. The number of total (P < 0.001), lateral (P = 0.019), and displaced (P < 0.001) rib fractures were significantly associated with delayed hemothorax. Lung contusions (P = 0.002), and initial minimal hemothorax (P < 0.001) and pneumothorax (P < 0.001) were more frequently associated with delayed hemothorax. Age (adjusted odds ratio (aOR) 1.03, 95% confidence interval (CI) 1.00–1.06, P = 0.022), mechanical ventilator use (aOR 9.67, 95% CI 1.01–92.75, P = 0.049), initial hemothorax (aOR 2.21, 95% CI 1.05–4.65, P = 0.037) and pneumothorax (aOR 2.99, 95% CI 1.36–6.54, P = 0.006), and displaced rib fractures (aOR 3.51, 95% CI 1.64–7.53, P = 0.001) were independently associated with delayed hemothorax.

Age, mechanical ventilation, initial hemo- or pneumothorax, and displaced rib fractures were risk factors for delayed hemothorax. Patients with these risk factors, and especially those with ≥2 displaced rib fractures, require close chest radiography follow-up of 2–30 days after the initial trauma.