P43. Validity of routine diagnostic tests for vertebral osteomyelitis/discitis and its influence by the infecting organism

BACKGROUND CONTEXT Spine surgeons rely on multiple tests to correctly diagnose adult vertebral osteomyelitis. Patient temperature, serum C- reactive protein (CRP), erythrocyte sedimentation rate (ESR) and serum polymorphonuclear leukocyte percentage (PMN%) are traditionally used as first-line tests because of their perceived high sensitivity for vertebral osteomyelitis. However, the influence of the infecting organism on the degree of marker elevation remains relatively unaddressed in the spine literature. It is possible each of these markers have a distinct sensitivity based on the infecting organism. PURPOSE The purpose of this study was to determine whether mean serum laboratory marker levels differed based on infecting organism and whether certain organisms are associated with greater elevated values. STUDY DESIGN/SETTING This was a retrospective institutional database review at the University of Missouri-Columbia from 2015-2019. PATIENT SAMPLE A total of 133 patients diagnosed with vertebral osteomyelitis who underwent blood culture, and/or biopsy prior to treatment. OUTCOME MEASURES ESR, CRP, WBC, PMN%, maximum temperature, culture organism. METHODS The mean peak inflammatory marker levels were compared among organisms with student\u0027s T test. Demographics, comorbidities and Charleston Comorbidity Index (CCI) were collected and multivariable logistic regression models were utilized. Receiver operating characteristic curve analysis was performed to delineate separate, optimal cut offs for CRP, ESR, WBC, and PMN% for patients with culture positive osteomyelitis. RESULTS Patients diagnosed with osteomyelitis had a max mean temperature of 37.2 C, CRP of 10.8 mg/L, ESR of 72 mm/hr, WBC of 12.1 cells/L, and PMN% of 74.1. A total of 105 patients (79%) had positive cultures. For CRP, Staphylococcus aureus (13.9 mg/L) and antibiotic resistant organisms (methicillin resistant Staphylococcus aureus and vancomycin-resistant Enterococci) (14.3 mg/L) had a higher mean value than culture negative cases (5.65 mg/L). For ESR, antibiotic resistant organisms (72.1 mm/hr) had a higher mean value than culture negative cases (57.9 mm/hr). For WBC, Staphylococcus aureus (14.4 cells/L), antibiotic resistant organisms (13.6 cells/L), and coagulase negative Staphylococcus (11.8 cells/L) had a higher mean value than culture negative cases (8.22 cells/L). For PMN%, Staphylococcus aureus (75.9%), antibiotic resistant organisms (77.2%), coagulase negative Staphylococcus (77.7%), and Streptococcus species (79.7%) had a higher mean peak value than culture negative cases (67.7%). Both Staphylococcus aureus (13.9 mg/L, 72.1 mm/hr, 14.4 cells/L, 75.9%) and antibiotic resistant organisms (14.3 mg/L, 94.0 mm/hr, 13.6 cells/L, 77.2%) had elevated CRP, ESR, WBC, and PMN% compared to fungal organisms (2.56 mg/L, 43.7 mm/hr, 8.17 cells/L, 64.0%). Temperature showed no significant differences in mean values among all organisms. Gram negative, Enterococcus, and fungal organisms did not show significant differences in mean values versus culture negative cases. CONCLUSIONS Serum laboratory markers in the diagnosis of vertebral osteomyelitis appear to be influenced by the infecting organism type. Laboratory values in patients diagnosed with vertebral osteomyelitis with culture negative or low-virulence organisms are lower compared to antibiotic resistant and Staphylococcus aureus organisms. Temperature did not correlate with a diagnosis of osteomyelitis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.