- OBJECTIVE: This study aimed to explore the early diagnostic value of lymphocyte count in the early diagnosis of surgical site in-fection (SSI) following posterior lumbar fusion.PATIENTS AND METHODS: In this study, we retrospectively analyzed the data from a total of 37 patients with lumbar SSI from Guizhou Prov-ince Orthopaedic Hospital and Nanyang Cen-tral Hospital, 2008.1-2018.11, and 104 patients without SSI. We analyzed the C-reactive pro-tein (CRP) level, white blood cell count (WBC) and differential count before instrumented lum-bar fusion at 3 and 7 days postoperatively. The significance of the differences was evaluated by one-way ANOVA, followed by Fisher's test. The parameters mentioned above were analyzed on postoperative days 3 and 7 using the receiver operating characteristic curve and the area un-der the curve (AUC). Furthermore, the analyses were conducted by SPSS 22.0 software.RESULTS: The lymphocyte count in the SSI group on postoperative day 3 was significant-ly lower than that in the no-SSI group after sur-gery (p=0.000). According to the ROC curve analysis of related parameters on postopera-tive day 3, the AUC value of lymphocytes (0.840) was significantly larger than the AUC value of C-reactive protein (0.749). CONCLUSIONS: The lymphocyte count and C-reactive protein level on postoperative day 3 are reliable predictors of infection.