From MedscapeCME Clinical Briefs
MMWR Morb Mortal Wkly Rep. 2010;59(RR-5):1-28.
News Author: Laurie Barclay, MD
CME Author: Charles P. Vega, MD
CME Released: 06/30/2010
Approximately one third of the world's population has latent tuberculosis infection, although the rate of latent tuberculosis has declined significantly during the last 30 years in the United States.
The lifetime risk for active tuberculosis among patients with a history of a positive tuberculin skin test result is between 5% to 10%, although the rate of active tuberculosis has also declined in the United States in the last decade.
Identifying patients with either active or latent tuberculosis infection is a public health priority, and the introduction of IGRAs may advance this effort.
IGRAs detect sensitization to M tuberculosis by measuring interferon gamma release in response to antigens presenting on M tuberculosis.
The current guidelines describe the accuracy of IGRAs and offer recommendations for the use of these assays.
* 4 IGRAs have been approved by the FDA for testing for tuberculosis. Assessing the accuracy of these tests is difficult because there is no "gold standard" to confirm latent tuberculosis infection or culture-negative tuberculosis.
* The sensitivity of the QFT-GIT test was 81% in detecting culture-confirmed active tuberculosis, whereas the pooled sensitivity for the T-Spot test was 91%. Both of these tests appear roughly similar to the tuberculin skin test in sensitivity to detect active tuberculosis.
* IGRAs are expected to be more specific than the tuberculin skin test because of reduced bias in interpretation and no interaction with the BCG vaccine. The pooled specificity values of QFT-GIT and T-Spot are 99% and 86%, respectively.
* Some research has suggested that IGRAs may be superior to tuberculin skin tests in diagnosing recent tuberculosis infections, whereas skin tests can be better in diagnosing remote infection. However, these studies are not unequivocal.
* IGRAs appear similar to the tuberculin skin test in predicting subsequent active tuberculosis.
* Few performance data exist for IGRA testing in children, particularly in high-risk children younger than 5 years.
* Limited data suggest that IGRAs are at least as accurate as tuberculin skin testing in detecting tuberculosis among immunocompromised persons.
* The authors recommend that IGRAs may be better than tuberculin skin tests among patients who are less likely to return for the reading of their skin tests (eg, among homeless individuals or patients who abuse drugs) and among those who previously received the BCG vaccine.
* Tuberculin skin testing is recommended vs IGRAs among children younger than 5 years.
* Either IGRAs or tuberculin skin testing may be used at the practitioners' discretion to test persons with recent contact with cases of active tuberculosis. Either test is also applicable to individuals with possible tuberculosis exposure in their workplace.
* In most cases, IGRAs and tuberculin skin tests should not be performed in the same person. Both tests may be done in high-risk cases in which the initial testing result was negative (probable false-negative) or in very low-risk cases with a positive initial test (probable false-positive).
* Neither test should generally be used among persons with a low risk for infection who are also unlikely to progress to active tuberculosis.
* The current recommendations suggest that IGRAs have a similar sensitivity but a greater specificity in diagnosing tuberculosis vs the tuberculin skin test.
* The current recommendations suggest that IGRAs are preferred vs tuberculin skin testing when the patient is less likely to return for reading of the skin test, or when the patient previously received the BCG vaccine. The tuberculin skin test remains preferred vs IGRAs among children younger than 5 years.