This study has some limitations. First, this study is conducted in a single-center and has a relatively small sample size in comparison with other multicenter researches. Second, the group, age range, disease diagnosis, and operation types were all relatively specific. Furthermore, the inclusion criteria of this study were not so strict and some comorbidities (such as arthritis, infections, and inflammatory diseases) might affect the results. Last, why the involved mechanisms preoperative CRP concentrations can serve as a predicator for POD still remains unclear.