The retrospective study enrolled 150 patients with bacterial infection in Zhongshan Hospital, Sun Yat-sen University, and the change of serum PCT level was monitored dynamically. Among them,100 patients suffered from recurrent infection, while the other 50 patients acquired effective treatment. The PCT levels of recurrent infection group and effective treatment group in the same period were observed, and the difference between them was analyzed. A total of 60 blood samples from healthy subjects were also collected, and the difference between recurrent turning points of PCT and PCT levels of healthy subjects was analyzed. The diagnostic performance of PCT, white blood cell (WBC) and interleukin 6 (IL-6) for recurrent infection with receiver operating characteristic (ROC) curve was evaluated, and a primary diagnostic cut-off value of PCT was established for recurrent infection.

In recurrent infection group and effective treatment group, the serum PCT levels showed different trends. The recurrent infection group showed an obvious rebound, and the level was higher than that in effective treatment group (P<0.05). The rebound turning points of serum PCT level in recurrent infection group were still higher than those in healthy subjects(P<0.05). The diagnostic significance of PCT for recurrent infection was confirmed by ROC curve analysis, and the area under the ROC curve for PCT was 83.5%. The most appropriate cut-off value was 2.29 ng/mL, and the sensitivity was 89.0%, the specificity was 83.0%, the positive predictive value was 84.0%, and the negative predictive value was 88.3%. The areas under the ROC curves of WBC and IL-6 for recurrent infection were 55.1% and 61.0%, respectively.

It was of great clinical application significance to monitor serum PCT level dynamically for the diagnosis and differential diagnosis of recurrent infection.