Interferon-gamma release assays (IGRAs) are significantly better than tuberculin skin tests (TST) at predicting progression from latent tuberculosis (TB), a new meta-analysis from Germany shows.
This means that patients with a positive IGRA, "especially if they belong to high risk groups for TB, will probably have a higher benefit when receiving preventive therapy in order to avoid TB disease later on than subjects scored positive by the TST," Dr. Roland Diel told Reuters Health by email.
Dr. Diel of Medical School Hannover and colleagues identified 28 publications to include in their study. Twenty-three covered commercial and "in house" IGRAs and 18 involved TSTs. The duration of follow-up ranged from one year to nearly four years. Twenty studies tracked patients for at least two years.
In all, 1,225 subjects were tested by "in house" IGRAs, 5,194 by commercial IGRAs and 8,479 by TST, according to a report online April 5th in Chest.
Overall, the positive predictive values were 2.7% for commercial IGRAs and 1.5% for TSTs. When only high-risk groups were considered, the corresponding values were 6.8% and 2.4%.
Both IGRAs and TST had high negative predictive values for progression (99.7% and 99.4%) but the IGRAs were still significantly better in this regard, according to the authors.
Dr. Diel pointed out that "just a very few patients with an initial negative IGRA or TST at baseline, also among immunosuppressed people, developed active tuberculosis during the period of observation."
"This is also highly important for tuberculosis control programs," he added, "because a test with a high negative predictive value means that therapy for latent tuberculosis can be limited to test-positive contacts without (the danger of overlooking) some who are truly infected but undetected by the tests."
Overall, the researchers conclude, "IGRAs provide significant benefits over the TST, but...the use of IGRAs, and testing for latent TB infection in general, should be targeted at high-risk groups."
The authors of the current report didn't address costs in their study. In 2009, however, when de Perio et al compared the cost-effectiveness of IGRAs and TSTs in screening health care workers, they found, "There was no prevalence of latent TB infection at which the TST became the most effective or least costly strategy."
SOURCE: http://bit.ly/KOcFvp
Chest 2012.
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