Postoperative C-Reactive Protein Trajectories in Spine Surgery – Influence of Vancomycin Powder: A Secondary Analysis of a Prospective Randomized Controlled Trial

Study Design Randomized controlled trial. Objectives To characterize postoperative C-reactive protein (CRP) trajectories as predictors of surgical site infection (SSI) following lumbar spine surgery, to determine optimal CRP thresholds, and to assess whether intrawound vancomycin powder affects postoperative CRP kinetics. Methods Data were drawn from a prospective randomized controlled trial enrolling 292 patients undergoing posterior lumbar interbody fusion. Patients received intrawound vancomycin powder (1 g) plus standard prophylaxis or standard prophylaxis alone. CRP was measured preoperatively and on days 1, 2, 3, 5, and 7. SSI was classified as overt (CDC criteria) or subclinical. ROC analysis evaluated prediction of any SSI at each time point. Results 22 patients (7.5%) developed any SSI: 9 overt (3.1%) and 13 subclinical (4.5%). CRP peaked at day 5 in the overall cohort. SSI patients showed persistently elevated CRP through day 7, while uncomplicated patients declined after day 3. Day 7 CRP showed the highest discriminatory ability (AUC = 0.813; cutoff ≥79 mg/L; sensitivity 61.1%; specificity 91.4%; NPV 95.2%). Vancomycin did not alter CRP kinetics at any time point (all P > 0.08). Conclusions In 292 spine surgery patients, day 7 CRP (AUC = 0.813) was the strongest predictor of any SSI. A cutoff of 79 mg/L on day 7 provided NPV of 95.2%, supporting CRP as a rule-out biomarker. Day 3 CRP ≥92 mg/L (AUC = 0.761) offers early warning capability. CRP trajectories did not differ significantly between the vancomycin and control groups. ClinicalTrials.gov: NCT02631408; EudraCT: 2014-002096-29.