13. The diagnostic utility of biomarkers: spinal instability or underlying infection

Abstract

<h3>BACKGROUND CONTEXT</h3> Surgical site infection is a devastating complication of surgery that increases morbidity for patients undergoing spinal surgery. However, diagnosis in some cases remains challenging often requiring a trip to the operating room to obtain cultures. Current literature has provided evidence that preoperative blood markers are diagnostic of infection in patients undergoing hip arthroplasty and total knee replacement, but there has been limited investigation on biomarker diagnostic utility in patients undergoing spinal surgery. <h3>PURPOSE</h3> To identify the diagnostic utility of laboratory markers to diagnose postoperative spinal infection. <h3>STUDY DESIGN/SETTING</h3> Retrospective case-control analysis <h3>PATIENT SAMPLE</h3> Patients having undergone prior spine surgery with a confirmed positive intraoperative culture during revision for presumed infection. An additional aseptic cohort was established with patients undergoing revision surgery for reasons other than infection. <h3>OUTCOME MEASURES</h3> White blood cell (WBC), erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), mean platelet volume (MPV), platelet number, MPV/platelet ratio, diagnostic sensitivity, specificity and threshold values for the diagnosis of spinal infection. <h3>METHODS</h3> A retrospective review was conducted at a single center academic hospital. Patients undergoing spinal fusion with a diagnosis of surgical site infection (SSI) from the dates of 2013 to 2019 were identified. In the aseptic cohort, any individual that had overt signs of infection or had infection within one year of revision procedure was excluded. Patients with a history of cancer, trauma, autoimmune disease on suppressive therapy, or noncompliance with medical therapy were excluded. WBC, ESR, CRP, MPV, MPV/Platelet ratio and demographic data was compared between groups and an AUC analysis was performed to determine threshold values. <h3>RESULTS</h3> A total of 418 patients were included, 224 in the aseptic cohort and 194 in the infection cohort. In terms of baseline demographics, there were significant differences between the cohorts in BMI, CCI, and ASA (p<0.05). BMI in the infection cohort was found to be greater than the aseptic cohort with a mean value of 33.7 vs 30.9 respectively. CCI and ASA was also elevated in the infections cohort as compared to the aseptic cohort with mean values of 3.84 for CCI and 2.90 for ASA as compared to 1.08 and 2.45 in the aseptic cohort. Significant differences were found between the cohorts with respect to MPV/platelet ratios, platelet number, MPV, CRP, ESR and WBC (p<0.01). Platelet ratio, platelet number, CRP, ESR and WBC were all greater in the infection group as compared to the aseptic group (platelet ratio 36.1 vs 24.7, platelet number 347 vs 249, CRP 9.99 vs 4.81, ESR 76.6 vs 46.5, WBC 9.87 vs 7.82 p<0.01) These differences were used to determine predictive cutoffs. The most sensitive markers for predicting postoperative infection were platelet number (cutoff 284 AUC 0.751; sensitivity 0.662) and ESR (cutoff 40.00 AUC 0.715; sensitivity 0.838). The most specific markers for predicting postoperative infection were platelet ratio (cutoff 31.02 AUC 0.758; specificity 0.842) and platelet count (cutoff 284.00 AUC 0.715; specificity 0.804). <h3>CONCLUSIONS</h3> This study concluded that preoperative platelet number and ESR are best used as screening measures, while MPV/platelet ratio and count are useful confirmatory markers. Further analysis will allow for a more depth investigation into optimal combination of biomarkers to result in the greatest diagnostic utility, but this initial report serves as evidence that preoperative biomarker collection may be a valuable tool to confirm the diagnosis in suspected postoperative surgical site infections. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.