MIAMI — Cost and other challenges need to be overcome before interferon-gamma release assays are adopted for widespread tuberculosis testing in children, according to Dr. John Bradley.
Although interferon-gamma release assays (IGRAs) are more accurate than standard tuberculin skin tests, they require 2–5 cc of blood, which can be a challenge in some children, Dr. Bradley said.
In addition, the accuracy of IGRAs is not well studied for children with latent TB infection, miliary TB or other disseminated infections, or active infections such as meningitis.
“There are insufficient data at present to recommend switching from tuberculin skin testing to an IGRA blood test for all kids,” Dr. Bradley said at a pediatric update sponsored by Miami Children's Hospital.
Also, “there are insufficient data to recommend a specific IGRA test,” said Dr. Bradley, an editor of the 2010 Red Book who is also with the division of infectious diseases, Rady Children's Hospital, San Diego.
There is a role for IGRA tests in specific clinical situations, however, Dr. Bradley said. For example, if a physician believes a parent is unlikely to return for the reading of a tuberculin skin test result, the IGRA may be indicated. In addition, the blood test is preferred for Bacillus Calmette-Gurin–immunized children with a positive tuberculin skin test result, as well as for a child with a positive skin test with no known exposures (these are presumed to be false-positive tuberculin skin tests, he said).
“Although the [IGRA] test is clearly an advance, it's not a perfect solution,” Dr. Bradley pointed out.
The two Food and Drug Administration–cleared IGRAs (QuantiFERON-TB Gold, Cellestis; T-SPOT.TB, Oxford Immunotec Ltd.) measure an in vitro lymphocyte response to Mycobacterium tuberculosis proteins.
“We believe the IGRA is a more sensitive test,” Dr. Bradley said. However, “they cost a lot more, so we're not ready to recommend them for widespread use.”
The tuberculin skin test remains the recommended TB assay in the 2010 Red Book, Dr. Bradley said, despite its having some limitations.
The immune competence of the child can impact the sensitivity, for example.
In addition, tuberculin skin tests are difficult to place intradermally, and if they are not intradermal, physicians cannot interpret them, he said. “Uncooperative, screaming children are challenges [also]. Two- and three-year-olds can be contortionists.”
Disclosures: Dr. Bradley said that he had no relevant financial conflicts