A Comparative Analysis of Drain Fluid and Serum Inflammatory Markers for Early Detection and Diagnosis of Surgical Site Infection Following Complex Orthopaedic Trauma Surgery: A Prospective Study

ObjectiveThis study aimed to evaluate and compare the diagnostic performance of postoperative drain fluid and serum inflammatory markers -specifically C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and total leukocyte count (TLC) -for the early detection of surgical site infection (SSI) following complex orthopaedic trauma surgery. MethodsThis prospective observational cohort study evaluated 150 patients undergoing complex orthopaedic trauma surgery requiring closed suction drain placement (study period: June 2023 to January 2024).Venous blood and drain fluid samples were collected systematically on postoperative days one (POD 1) and two (POD 2) prior to clinical SSI manifestation.Patients were followed prospectively for six months for SSI occurrence per Centers for Disease Control and Prevention (CDC) criteria.Inflammatory marker dynamics were compared between infected and non-infected groups.Receiver operating characteristic (ROC) curves and formal paired DeLong tests were performed to evaluate diagnostic accuracy. ResultsPostoperative SSI occurred in eight patients (5.3%; six superficial, two deep; 75.0%culture positivity).Patients who developed SSI demonstrated significantly higher serum and drain fluid inflammatory markers on both POD 1 and POD 2 compared with non-infected patients (p < 0.001).Drain fluid CRP on POD 1 demonstrated superior diagnostic accuracy (area under the ROC curve (AUC) = 0.93; 95% confidence interval (CI): 0.87-0.99;sensitivity: 87.5%, specificity: 90.8% at cutoff > 120 mg/L) compared to paired serum CRP (AUC = 0.82; 95% CI: 0.71-0.93;sensitivity: 75.0%, specificity: 78.2%), confirmed by DeLong's test (Z = 2.07, p = 0.038).Univariate analysis identified operative duration > 3 hours, diabetes mellitus, POD 1 drain output > 100 mL, and elevated POD 1 drain fluid CRP as significant exploratory factors associated with SSI. ConclusionsIn this cohort, POD 1 drain fluid CRP demonstrated a promising diagnostic association with early SSI following complex orthopaedic trauma surgery, outperforming paired serum CRP.However, given the exploratory single-center design and limited outcome event count, its incremental clinical value, optimal thresholds, and safety require prospective multi-center validation before routine clinical implementation can be considered.