Change in Bone CT Attenuation and C-reactive Protein Are Predictors of Bone Biopsy Culture Positivity in Patients With Vertebral Discitis/Osteomyelitis

Study Design.Case-control study.Objective.The objective of this study was to identify the best laboratory and imaging factors to predict bone biopsy culture positivity in the setting of vertebral discitis/osteomyelitis (VDO).Summary of Background Data.Good predictors of bone biopsy culture positivity in the setting of VDO are unknown.Methods.Retrospective review was performed for 46 patients who underwent CT-guided bone biopsy for the evaluation of clinically confirmed VDO. Erythrocyte sedimentation rate, C-reactive protein (CRP), mean CT attenuation of the biopsied bone, and the change in the CT attenuation of the bone compared to unaffected vertebral bone (delta CT attenuation) were measured. Receiver-operator characteristic curve analyses were performed to identify the optimal threshold value for each variable. A multivariable logistic regression model was used to predict the probability of a positive bone culture using delta CT attenuation and CRPx100% fold above normal.Results.For one of the 46 VDO patients, bone cultures were not obtained. Approximately 35.6% (16/45) of bone cultures were positive. The most significant predictors of bone culture positivity were CRP x100% fold above normal (P = 0.011) and delta CT attenuation (P = <0.001). Optimized predictive thresholds were calculated to be CRP 4-fold above normal reference value (90.9% sensitivity, 73.7% specificity), or if the CT attenuation of the affected vertebral body was >25.9 HU lower relative to unaffected bone (93.8% sensitivity, 75.0% specificity).Conclusion.Delta CT attenuation, as well as CRP level over four times the upper limits of normal, were the strongest predictors for bone culture positivity in patients with VDO.Level of Evidence: 3.