Normal Range of the Inflammation Related Laboratory Findings and Predictors of the Postoperative Infection in Spinal Posterior Fusion Surgery

BACKGROUND: Inflammation related hematological parameters vary greatly depending on patients. It is not well known how much increase of which parameter warrants suspicion of postoperative infection. This study proposes to identify the normal range and the predictive factors for postoperative infection by conducting a time series analysis of the hematological parameters of patients after the spinal posterior fusion. METHODS: A retrospective study was done with 608 patients who underwent spinal posterior fusion with pedicle screw fixation. Laboratory assessment including the leucocyte, neutrophil, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) of patients for 2 weeks after operation. The patients were divided into the one-level fusion group (group I), the two-level fusion group (group II), the three or multi-level fusion or reoperation group (group III), and the postoperative infection group (group IV). Blood was drawn before breakfast prior to the operation, and then 2-3 days, 4-7 days, 8-11 days, and 12-14 days after the operation. The leucocyte count, neutrophil count, CRP, and ESR were measured. RESULTS: From 4-7 days after the operation, the CRP and neutrophil count of group IV were significantly higher than those of group I and II, and from 8-11 days after operation, the CRP and neutrophil counts were significantly higher than those of all groups. Twelve to fourteen days after the operation, the neutrophil count of group IV was significantly higher than that of group I and II, while the neutrophil count of group III was also higher than that of group I. The lower limit of the 95% confidence interval (CI) of the CRP and neutrophil count group IV was greater than the upper limit of the 95% CI of group I and II. The ESR of group IV was significantly higher than that of group I and III. CONCLUSIONS: If the postoperative CRP and neutrophil counts are high, or if the CRP begins to rise again 8 days after the operation, the likelihood of infection increases, but caution must be exercised in interpreting the results. If the hematological parameters are higher than the lower limit of the 95% CI of the postoperative infection group, infection must be strongly suspected.