• Eiichiro Iwata, Hideki Shigematsu, Munehisa Koizumi, Hiroshi Nakajima, Akinori Okuda, Yasuhiko Morimoto, Keisuke Masuda, Yusuke Yamamoto, and Yasuhito Tanaka.
• Department of Orthopedic Surgery, Nara Medical University, Nara, Japan.
• Spine. 2016 Jul 15; 41 (14): 1173-1178.

Study DesignA case-control study.ObjectiveThe objective of this study is to identify biochemical markers for surgical site infection (SSI) in posterior instrumented spinal fusion that are not affected by operative circumstances and to determine diagnostic cutoffs for these markers.Summary Of Background DataNumerous biochemical markers may be used for early detection of SSI; however, these markers may be affected by operative factors.MethodsWe reviewed data on C-reactive protein level and total white blood cell count and differential count before instrumented spinal fusion and at 1, 4, and 7 days postoperatively. The 141 patients in our sample were divided into an SSI group (patients who developed deep SSI) and a no-SSI group. We determined which markers differed significantly between groups and identified those not affected by operative circumstances (operating time, intraoperative blood loss, number of fusion segments) in the no-SSI group. Then, we determined diagnostic cutoffs for these unaffected markers by using receiver-operating characteristic curves.ResultsThree markers were selected: lymphocyte count at 4 days postoperatively (cutoff 1180/μL, sensitivity 90.9%, specificity 65.4%, area under the curve [AUC] 0.80), lymphocyte count of at 7 days postoperatively (cutoff <1090/μL, sensitivity 63.6%, specificity 78.5%, AUC 0.77), and C-reactive protein level at 7 days postoperatively (cutoff >4.4 mg/dL, sensitivity 90.9%, specificity 89.2%, AUC 0.95).ConclusionLymphocyte count at 4 and 7 days postoperatively and C-reactive protein level at 7 days postoperatively are reliable markers for SSI following instrumented spinal fusion. Lymphocyte count at 4 days should be useful for screening because of its high sensitivity and because it can be measured early. C-reactive protein level at 7 days should be useful for definitive diagnosis given its high sensitivity and specificity and large AUC.Level Of Evidence4.

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