title: Use of interferon-gamma release assays in a health care worker screening program: experience from a tertiary care centre in the United States.
abstract: BACKGROUND
  Interferon-gamma release assays including the QuantiFERON-TB Gold In-Tube test (QFT-GIT [Cellestis Ltd, Australia]) may be used in place of the tuberculin skin test (TST) in surveillance programs for Mycobacterium tuberculosis infection control. However, data on performance and practicality of the QFT-GIT in such programs for health care workers (HCWs) are limited.
  
  
  OBJECTIVE
  To assess the performance, practicality and reversion rate of the QFT-GIT among HCWs at a tertiary health care institution in the United States.
  
  
  METHODS
  Retrospective chart review of HCWs at Central Arkansas Veterans Healthcare System (Arkansas, USA) who underwent QFT-GIT testing as a part of their employee screening between November 1, 2008 and October 31, 2009.
  
  
  RESULTS
  QFT-GIT was used to screen 3290 HCWs. The initial QFT-GIT was interpreted as positive for 129 (3.9%) HCWs, negative for 3155 (95.9%) and indeterminate for six (0.2%). Testing with QFT-GIT was repeated in 45 HCWs who had positive results on the initial test. The QFT-GIT reverted to negative in 18 (40.0%) HCWs, all of whom had negative TST status and initial interferon-gamma values of 0.35 IU⁄mL to 2.0 IU⁄mL.
  
  
  CONCLUSIONS
  The QFT-GIT test is feasible in large health care setting as an alternative to TST for M tuberculosis infection screening in HCWs but is not free from challenges. The major concerns are the high number of positive test results and high reversion rates on repeat testing, illustrating poor short-term reproducibility of positive QFT-GIT test results. These results suggest adopting a borderline zone between interferon-gamma values of 0.35 IU⁄mL to 2.0 IU⁄mL, and cautious clinical interpretation of values in this range.
authors.affiliation: Pulmonary and Critical Care Division, University of Arkansas for Medical Sciences, Little Rock, AR, USA. manish.joshi@va.gov
authors.forename: Manish
authors.initials: M
authors.lastname: Joshi
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Monson
authors.forename: Gail L
authors.initials: GL
authors.lastname: Woods
mesh_terms: D000328:Adult; D005240:Feasibility Studies; D005260:Female; D006282:Health Personnel; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D059425:Interferon-gamma Release Tests / Q000379:methods*; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D012189:Retrospective Studies; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis*; D014481:United States
chemical_list: D007371:Interferon-gamma