Tuberculin Skin Test Versus the Interferon-γ Release Assays: Out With the Old, In With the New

* Abbreviations: BCG — : Bacillus Calmette-Guerin IGRA — : interferon-γ release assay QFT — : QuantiFERON-TB Gold In-Tube TST — : tuberculin skin test The tuberculin skin test (TST) for determining if a person is infected with Mycobacterium tuberculosis has been the dominant test for a century. The interferon-γ release assays (IGRAs) have been available for a decade; dozens of studies have compared the performance of the 2 types of tests in a variety of settings. The advantages of the IGRAs have led some experts to recommend the “retirement” of the TST, even in pediatrics.1 However, the best use of the IGRAs in young children remains controversial because of a paucity of data.2 Both test types depend on the cellular immune response to mycobacterial antigens. Purified protein derivative, the solution used in the TST, has dozens of antigens, some of which are also found on many species of nontuberculous mycobacteria and the Bacillus Calmette-Guerin (BCG) vaccines, leading to low test specificity. The IGRAs use only 2 or 3 antigens that do not cross-react with most nontuberculous mycobacteria and BCG and consistently have higher specificity than the TST.3 Unfortunately, both test types have lower sensitivity in individuals with diminished cellular immunity who are at high risk of having tuberculosis infection progress to disease, and neither test type … Address correspondence to Jeffrey R. Starke, MD, FAAP, Baylor College of Medicine, Texas Children’s Hospital, MC 3-2371, Bates Ave, Houston, TX 77030. E-mail: jstarke{at}bcm.edu