The World Health Organization (WHO) has opened the door to widespread use of interferon gamma release assays (IGRAs) in testing for tuberculosis (TB) infection. Officials lifted restrictions on the use of the assays as part of an update to guidelines on the management of latent TB infections.
The WHO recommended against using IGRAs in low- to middle-income countries in 2011. That ruling was based on evidence IGRAs and tuberculin skin tests (TSTs) perform comparably. With IGRAs being more expensive and more technically complex than TSTs, the WHO recommended using the skin tests in “resource-constrained settings.” The WHO recommended both tests for use in wealthier countries.
Seven years later, the WHO has revised its position. The new guidelines (PDF) suggest TST and IGRA as options for latent TB testing, regardless of the wealth or disease prevalence of the country. That shifts the decision-making power from the WHO to clinicians and program managers on the ground.
The WHO made the change despite still having reservations about IGRAs. A review failed to find strong evidence that IGRAs are better than TSTs at predicting progression from latent to active TB. And that TSTs “may require significantly fewer resources” than IGRAs, which need fairly sophisticated infrastructure and technical expertise. The problem is TSTs are in short supply.
“Recurrent global shortages and stock-outs of TST reduce its use in scaling up programmatic management of [latent TB],” the WHO wrote in its guidelines. “The global shortage of TST should be addressed urgently.”
The WHO wants work to address the shortage of TST to advance in parallel to the development of tests that perform better than either of the existing options. TST and IGRA both have weaknesses and can deliver false-negative results. The WHO wants to see more investment to support research into tests that make better predictions than IGRA and TST.
Until those tests hit the market, the guidelines could benefit the two commercial suppliers of IGRAs, namely Qiagen and Oxford Immunotec. Qiagen welcomed the changes to the guidelines, adding that it is “supporting efforts to simplify the [latent TB] screening cascade of care using diagnostic tests and risk-based testing.”