title: High rate of negative results of tuberculin and QuantiFERON tests among individuals with a history of positive skin test results.
abstract: OBJECTIVE
  To evaluate individuals at high risk for tuberculosis exposure who had a history of a positive tuberculin skin test (TST) result in order to determine the prevalence of unsuspected negative TST results. To confirm these findings with the QuantiFERON-TB test (QFT), an in vitro whole-blood assay that measures tuberculin-induced secretion of interferon-gamma.
  
  
  METHODS
  This survey was conducted from November 2001 through December 2003 at 3 sites where TST screening is regularly done. Detailed histories and reviews of medical records were performed. TSTs were placed and read by 2 experienced healthcare workers, and blood was drawn for QFT. Any subject with a negative result of an initial TST during the study (induration diameter, <10 mm) underwent a second TST and a second QFT. The TST-negative group comprised individuals for whom both TSTs had an induration diameter of <10 mm. The confirmed-negative group comprised individuals for whom both TSTs yielded no detectable induration and results of both QFTs were negative.
  
  
  RESULTS
  A total of 67 immunocompetent subjects with positive results of a previous TST were enrolled in the study. Of 56 subjects who completed the TST protocol, 25 (44.6%; 95% confidence interval [CI], 31.6%-57.6%) were TST negative (P<.001). Of 31 subjects who completed the TST protocol and the QFT protocol, 8 (25.8%; 95% CI, 10.4%-41.2%) were confirmed negative (P<.005).
  
  
  CONCLUSIONS
  A significant proportion of subjects with positive results of a previous TST were TST negative in this study, and a subset of these were confirmed negative. These individuals' TST status may have reverted or may never have been positive. It will be important in future studies to determine whether such individuals lack immunity to tuberculosis and whether they should be considered for reentry into tuberculosis screening programs.
authors: Pulmonary and Critical Care Section, Department of Medicine, Yale University School of Medicine, New Haven, CT 06520-8057, USA. Lloyd.Friedman@milfordhospital.org
authors: Lloyd N
authors: LN
authors: Friedman
authors: Esther R
authors: ER
authors: Nash
authors: June
authors: J
authors: Bryant
authors: Susan
authors: S
authors: Henry
authors: Julia
authors: J
authors: Shi
authors: Joyce
authors: J
authors: D'Amato
authors: Ghada H
authors: GH
authors: Khaled
authors: Mark B
authors: MB
authors: Russi
authors: Patrick G
authors: PG
authors: O'Connor
authors: Stephen C
authors: SC
authors: Edberg
authors: Margaret A
authors: MA
authors: Pisani
authors: Hilary C
authors: HC
authors: Cain
authors: Lynn
authors: L
authors: Tanoue
authors: David N
authors: DN
authors: Weissman