Abstract: Background: Fracture-related infection (FRI) represents a significant post-traumatic complication, with diagnosis often hindered by its heterogeneous clinical presentation, and differentiating FRI from non-infectious conditions can be difficult. Aim: This study aimed to investigate the relationship between the expression of immune markers CD64 and CD66b on monocytes and neutrophils in patients with FRI, focusing on postoperative changes. Methods:Blood samples were collected from 72 patients suspected of having FRI in closed fractures, including 11 positive and 63 negative cases. Flow cytometry was used to measure the fluorescent intensities of CD64 and CD66b on neutrophils and monocytes. The ratio of CD64/CD66b was calculated to further explore the relationship between these markers. Results: The analysis revealed that the CD64/CD66b ratio differed significantly between preoperative and postoperative measurements in FRI-positive patients. This change in immune marker expression was more pronounced in patients with confirmed infections, suggesting that these markers may be indicative of infection dynamics after fracture healing. Additionally, delayed fracture healing was found to influence immune response, affecting marker expression. The study also identified that the expression ratios of NCD64/NC66b (neutrophil CD64 to CD66b) and MCD64/MCD66b (monocyte CD64 to CD66b) were valuable in predicting FRI presence. Conclusion: The study provides evidence that NCD64/NC66b and MCD64/MCD66b ratios are potential suggestive diagnostic biomarkers for FRI. Changes in the expression of these markers, particularly after surgery, reflect infection status and may aid in the diagnosis and management of FRI, offering insights into infection progression and fracture healing in adult patients.
