title: C reactive protein, erythrocyte sedimentation rate, or both, in the diagnosis of atraumatic paediatric limb pain?
abstract: OBJECTIVE
  To assess if measurement of either C reactive protein (CRP) or erythrocyte sedimentation rate (ESR) individually has an equivalent diagnostic value to measurement of both in identifying orthopaedic infection as the cause of paediatric atraumatic limb pain.
  
  
  METHODS
  Emergency department of a paediatric teaching hospital.
  
  
  METHODS
  Retrospective study of case notes for patients attending the emergency department with a complaint of atraumatic limb pain and in whom both ESR and CRP were measured at the time of presentation. Laboratory results at the time of presentation were recorded along with the final diagnosis. Receiver operating characteristic (ROC) curves were created using the data and the optimum cut-off values for each of ESR and CRP were derived using the point of best trade off between sensitivity and specificity. Likelihood ratios for ESR and CRP individually and in combination were calculated.
  
  
  RESULTS
  259 patients were included in the study, of whom 17 were considered to have an orthopaedic infection. ROC curves revealed the best results were obtained using cut-off values of CRP >7 and ESR >12. The combination of a CRP >7 and an ESR >12 gave the best positive likelihood ratio at 6.26 (likelihood ratio 5.34 (CRP >7) vs 2.57 (ESR >12)). For ruling out disease, the combination of CRP ≤7 and ESR ≤12 also outperformed either variable individually (negative likelihood ratio 0.09 (CRP ≤7 and ESR ≤12) vs 0.34 (CRP ≤7) vs 0.18 (ESR ≤12)).
  
  
  CONCLUSIONS
  Measurement of both CRP and ESR should be considered an important aid in the investigation of atraumatic limb pain.
authors.affiliation: Emergency Department, Edinburgh Royal Infirmary, 51 Little France Crescent, Edinburgh, EH16 4SA UK. psrobinson@doctors.org.uk
authors.forename: Sara
authors.initials: S
authors.lastname: Robinson
authors.forename: Paul
authors.initials: P
authors.lastname: Leonard
mesh_terms: D015415:Biomarkers / Q000097:blood; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D004636:Emergency Service, Hospital; D005121:Extremities; D005260:Female; D006801:Humans; D007239:Infections / Q000097:blood / Q000175:diagnosis*; D016013:Likelihood Functions; D008297:Male; D010146:Pain / Q000097:blood / Q000175:diagnosis*; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein