title: Should gram stains have a role in diagnosing hip arthroplasty infections?
abstract: BACKGROUND
  The utility of Gram stains in diagnosing periprosthetic infections following total hip arthroplasty has recently been questioned. Several studies report low sensitivity of the test, and its poor ability to either confirm or rule out infection in patients undergoing revision total hip arthroplasty. Despite this, many institutions including that of the senior author continue to perform Gram stains during revision total hip arthroplasty.
  
  
  OBJECTIVE
  We assessed the sensitivity, specificity, accuracy, and positive and negative predictive values of Gram stains from surgical-site samplings taken from procedures on patients with both infected and aseptic revision total hip arthroplasties.
  
  
  METHODS
  A review was performed on patients who underwent revision total hip arthroplasty between 2000 and 2007. Eighty-two Gram stains were performed on patients who had infected total hip arthroplasties and underwent revision procedures. Additionally, of the 410 revision total hip arthroplasties performed on patients who were confirmed infection-free, 120 Gram stains were performed. Patients were diagnosed as infected using multiple criteria at the time of surgery. Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated from these Gram stain results.
  
  
  RESULTS
  The Gram stain demonstrated a sensitivity and specificity of 9.8% and 100%, respectively. In this series, the Gram stain had a negative predictive value of 62%, a positive predictive value of 100%, and an accuracy of 63%.
  
  
  CONCLUSIONS
  Gram stains obtained from surgical-site samples had poor sensitivity and poor negative predictive value. Based on these findings, as well as those of other authors, we believe that Gram stains should no longer be considered for diagnosing infections in revision total hip arthroplasty.
  
  
  METHODS
  Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Reconstruction, Sinai Hospital of Baltimore, 2401 West Belvedere Avenue, Baltimore, MD 21215, USA.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Johnson
authors.forename: Michael G
authors.initials: MG
authors.lastname: Zywiel
authors.forename: D Alex
authors.initials: DA
authors.lastname: Stroh
authors.forename: David R
authors.initials: DR
authors.lastname: Marker
authors.forename: Michael A
authors.initials: MA
authors.lastname: Mont
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation; D004396:Coloring Agents; D019992:Databases as Topic; D005188:False Negative Reactions; D005189:False Positive Reactions; D005840:Gentian Violet; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D010619:Phenazines; D011237:Predictive Value of Tests; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000382:microbiology / Q000601:surgery; D012086:Reoperation; D012680:Sensitivity and Specificity; D013194:Staining and Labeling / Q000379:methods*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D004396:Coloring Agents; C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet