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Assay comparable with TST in diagnosing TB in children at high risk for illness
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An interferon-gamma release assay may be comparable with the traditionally used tuberculin skin test in children who are at high risk for tuberculosis and may be more specific in children who have received the bacille Calmette-Guérin vaccine, according to a study published online.
Andrea T. Cruz, MD, MPH, of Baylor College of Medicine in Houston, and colleagues prospectively studied 210 children between the ages of 1 month and 18 years who were referred to the Memorial Hermann Children’s, Lyndon B. Johnson General and Ben Taub General hospitals in Houston in 2005 and 2006. All children were tested using the T-Spot.TB blood test (Oxford Immunotec) and the tuberculin skin test (TST). Of those children who had been referred, 31 children were diagnosed with active TB and 110 children had latent infection.
In 13 of the children who were diagnosed with culture-confirmed TB, the sensitivity of the assay was 92% vs. 77% of TST results. Concordance was 69% between these two sets of results. For high-risk children, whom the researchers defined as having had contact with an active TB patient, concordance was higher at 94% for children who did not receive the bacille Calmette-Guérin (BCG) vaccine and 88% for BCG-immunized children. The researchers noted that for intermediate-risk children, whom they defined as children who had risk factors but no identifiable source case, concordance was lower at 74% for BCG-unimmunized children and 33% for BCG-immunized children. Concordance was lowest among low-risk children, whom the researchers defined as children as having no risk factors at all, at 74% for BCG-unimmunized children and 20% for BCG-immunized children.
“T-Spot.TB was more specific than the TST for children who were immunized with BCG and who were at intermediate risk for [latent TB infection], a population for which optimizing specificity can decrease the need for unnecessary interventions,” Cruz and colleagues wrote.
The researchers added that although the TST has been used for a decade, the test lacks the desired sensitivity and specificity.
“The negative predictive value can be diminished by false negatives seen in young children and in immunocompromised individuals, with corticosteroid administration, or in people with overwhelming tuberculosis disease,” the researchers wrote in their study. “Conversely, the positive predictive value of the TST can be decreased by false positives caused by exposure to nontuberculous mycobacteria and cross-reactivity with the BCG vaccine.”
For more information:
- Cruz AT. Pediatrics. 2010;doi:10.1542/peds.2010-1725.