title: C-reactive protein is a more sensitive and specific marker for diagnosing bacterial infections in systemic lupus erythematosus compared to S100A8/A9 and procalcitonin.
abstract: OBJECTIVE
  C-reactive protein (CRP), S100A8/A9, and procalcitonin have been suggested as markers of infection in patients with systemic lupus erythematosus (SLE). We investigated the clinical significance of these factors for indication of infection in SLE.
  
  
  METHODS
  Blood samples were prospectively collected from 34 patients with SLE who had bacterial infections and 39 patients with SLE who had disease flares and no evidence of infection. A second set of serum samples was collected after the infections or flares were resolved.
  
  
  RESULTS
  CRP levels of SLE patients with infections were higher than those with flares [5.9 mg/dl (IQR 2.42, 10.53) vs 0.06 mg/dl (IQR 0.03, 0.15), p < 0.001] and decreased after the infection was resolved. S100A8/A9 and procalcitonin levels of SLE patients with infection were also higher [4.69 μg/ml (IQR 2.25, 12.07) vs 1.07 (IQR 0.49, 3.05) (p < 0.001) and 0 ng/ml (IQR 0-0.38) vs 0 (0-0) (p < 0.001), respectively]; these levels were also reduced once the infection disappeared. In the receiver-operating characteristics analysis of CRP, S100A8/A9, and procalcitonin, the area under the curve was 0.966 (95% CI 0.925-1.007), 0.732 (95% CI 0.61-0.854), and 0.667 (95% CI 0.534-0.799), respectively. CRP indicated the presence of an infection with a sensitivity of 100% and a specificity of 90%, with a cutoff value of 1.35 mg/dl.
  
  
  CONCLUSIONS
  Our data suggest that CRP is the most sensitive and specific marker for diagnosing bacterial infections in SLE.
authors.affiliation: Department of Rheumatology and BK21 Division of Cell Transformation and Restoration, Ajou University School of Medicine, San 5, Wonchon-dong, Yeongtong-gu, Suwon, South Korea 443-721.
authors.forename: Hyoun-Ah
authors.initials: HA
authors.lastname: Kim
authors.forename: Ja-Young
authors.initials: JY
authors.lastname: Jeon
authors.forename: Jeong-Mi
authors.initials: JM
authors.lastname: An
authors.forename: Bo-Ram
authors.initials: BR
authors.lastname: Koh
authors.forename: Chang-Hee
authors.initials: CH
authors.lastname: Suh
mesh_terms: D000328:Adult; D001424:Bacterial Infections / Q000097:blood* / Q000175:diagnosis* / Q000276:immunology; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis / Q000378:metabolism*; D002116:Calcitonin / Q000097:blood; D015740:Calcitonin Gene-Related Peptide; D040501:Calgranulin A / Q000097:blood; D040502:Calgranulin B / Q000097:blood; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology; D008297:Male; D009894:Opportunistic Infections / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D011237:Predictive Value of Tests; D011498:Protein Precursors / Q000097:blood; D055815:Young Adult
chemical_list: D015415:Biomarkers; C000606589:CALCA protein, human; D040501:Calgranulin A; D040502:Calgranulin B; D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein; D015740:Calcitonin Gene-Related Peptide