title: Absence of interferon-gamma release assay conversion following tuberculin skin testing.
abstract: BACKGROUND
  The tuberculin skin test (TST) has been the established screening method for tuberculosis (TB) for over a century. Interferon-gamma release assays (IGRAs) using Mycobacterium tuberculosis-specific antigens are increasingly used as diagnostic tests for TB. Tuberculin comprises multiple antigens, including the antigens used in the QuantiFERON-TB Gold In-Tube (QFT-GIT) assay. Exposure to these antigens by means of a TST may prime an immune response that leads to a false-positive result in a subsequent IGRA, limiting the validity of IGRAs in patients in whom these tests are performed sequentially. The current data on the influence of prior TST on IGRAs show inconsistent results.
  
  
  METHODS
  Sixteen non-bacille Calmette-Guérin immunised medical students with no history of TB exposure and minimal risk of exposure to TB during the study period were tested simultaneously with a TST and QFT-GIT. The QFT-GIT assay was repeated 6 and 10 weeks later.
  
  
  RESULTS
  At baseline, all TST and QFT-GIT results were negative and remained negative 6 and 10 weeks after the TST.
  
  
  CONCLUSIONS
  These data show that negative QFT-GIT results are reproducible and suggest that a TST does not result in conversion of subsequent QFT-GIT assays in the absence of concomitant TB exposure. Therefore, a positive QFT-GIT should not be attributed to boosting induced by a previous TST.
authors.affiliation: Department of Paediatrics, The University of Melbourne, Royal Children's Hospital Melbourne, Parkville, Victoria, Australia. nicole.ritz@rch.org.au
authors.forename: N
authors.initials: N
authors.lastname: Ritz
authors.forename: C
authors.initials: C
authors.lastname: Yau
authors.forename: T G
authors.initials: TG
authors.lastname: Connell
authors.forename: M
authors.initials: M
authors.lastname: Tebruegge
authors.forename: D
authors.initials: D
authors.lastname: Leslie
authors.forename: N
authors.initials: N
authors.lastname: Curtis
mesh_terms: D000328:Adult; D000942:Antigens, Bacterial / Q000032:analysis*; D006801:Humans; D007118:Immunoassay; D007371:Interferon-gamma / Q000032:analysis*; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D015203:Reproducibility of Results; D013337:Students, Medical; D011795:Surveys and Questionnaires; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D000942:Antigens, Bacterial; D007371:Interferon-gamma