title: Performance characteristics of broth-only cultures after revision total joint arthroplasty.
abstract: BACKGROUND
  Surgeons frequently obtain intraoperative cultures at the time of revision total joint arthroplasty. The use of broth or liquid medium before applying the sample to the agar medium may be associated with contamination and false-positive cultures; however, the degree to which this is the case is not known.
  
  
  OBJECTIVE
  We (1) calculated the performance characteristics of broth-only cultures (sensitivity, specificity, positive predictive value, and negative predictive value) and (2) characterized the organisms identified in broth to determine whether a specific organism showed increased proclivity for true-positive periprosthetic joint infection (PJI).
  
  
  METHODS
  A single-institution retrospective chart review was performed on 257 revision total joint arthroplasties from 2009 through 2010. One hundred ninety (74%) had cultures for review. All culture results, as well as treatment, if any, were documented and patients were followed for a minimum of 1 year for evidence of PJI. Cultures were measured as either positive from the broth only or broth negative. The true diagnosis of infection was determined by the Musculoskeletal Infection Society criteria during the preoperative workup or postoperatively at 1 year for purposes of calculating the performance characteristics of the broth-only culture.
  
  
  RESULTS
  The sensitivity, specificity, positive predictive value, and negative predictive value were 19%, 88%, 13%, and 92%, respectively. The most common organism identified was coagulase-negative Staphylococcus (16 of 24 cases, 67%). Coagulase-negative Staphylococcus was present in all three true-positive cases; however, it was also found in 13 of the false-positive cases.
  
  
  CONCLUSIONS
  The broth-only positive cultures showed poor sensitivity and positive predictive value but good specificity and negative predictive value. The good specificity indicates that it can help to rule in the presence of PJI; however, the poor sensitivity makes broth-only culture an unreliable screening test. We recommend that broth-only culture results be carefully scrutinized and decisions on the diagnosis and treatment of infection should be based specifically on the Musculoskeletal Infection Society criteria.
  
  
  METHODS
  Level IV, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: The Rothman Institute at Thomas Jefferson University, 925 Chestnut Street, Philadelphia, PA, 19107, USA, research@rothmaninstitute.com.
authors.forename: Eric B
authors.initials: EB
authors.lastname: Smith
authors.forename: Jenny
authors.initials: J
authors.lastname: Cai
authors.forename: Rachael
authors.initials: R
authors.lastname: Wynne
authors.forename: Mitchell
authors.initials: M
authors.lastname: Maltenfort
authors.forename: Robert P
authors.initials: RP
authors.lastname: Good
mesh_terms: D001170:Arthritis, Infectious / Q000175:diagnosis* / Q000382:microbiology*; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects; D003470:Culture Media; D019317:Evidence-Based Medicine; D005189:False Positive Reactions; D005500:Follow-Up Studies; D006801:Humans; D008828:Microbiological Techniques / Q000592:standards*; D016343:Monitoring, Intraoperative / Q000379:methods; D011237:Predictive Value of Tests; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000382:microbiology*; D012086:Reoperation; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013210:Staphylococcus / Q000302:isolation & purification
chemical_list: D003470:Culture Media