Effect of Tuberculin Skin Test on Ex-vivo Interferon-gamma Assay for Latent Tuberculosis Infection.

Lee, Jung Yeon; Choi, Hee Jin; Cho, Sang Nae; Park, I Nae; Oh, Yeon Mok; Lee, Sang Do; Kim, Woo Sung; Kim, Dong Soon; Kim, Won Dong; Shim, Tae Sun

doi:2005.59.4.406

Tuberc Respir Dis > Volume 59(4); 2005 > Article

Original Article

Tuberculosis and Respiratory Diseases 2005;59(4):406-412.
DOI: https://doi.org/10.4046/trd.2005.59.4.406 Published online October 1, 2005.

Effect of Tuberculin Skin Test on Ex-vivo Interferon-gamma Assay for Latent Tuberculosis Infection.

Jung Yeon Lee, Hee Jin Choi, Sang Nae Cho, I Nae Park, Yeon Mok Oh, Sang Do Lee, Woo Sung Kim, Dong Soon Kim, Won Dong Kim, Tae Sun Shim

¹Division of Pulmonary and Critical Care Medicine, University of Ulsan College of Medicine, Korea. shimts@amc.seoul.kr
²Asan Medical Center, Asan Institute for Life Sciences, Korea.
³Department of Microbiology, Yonsei University College of Medicine, Korea.

Abstract

BACKGROUND
Recently, two commercialized whole-blood assays, QuantiFERON(R)-TB Gold (QFT) and T SPOT-TB(R)(SPOT), which measure the IFN-gamma released in the whole blood after being incubation with mycobacterial antigens, were approved for the diagnosis of a latent tuberculosis infection (LTBI). However, there is data on whether or not the previously used PPD skin tests (TST) have any influence on the diagnostic ability of these ex-vivo IFN-gamma assays. METHOD: Forty-six 15 year-old students who did not appear to be infected with Mycobacterium tuberculosis were enrolled in this study. The peripheral blood was collected and used for two IFN-gamma assays. The IFN-gamma assays and TST were performed at the baseline (1st). The TST was repeated two months later (2nd), and the IFN-gamma assays were repeated two (2nd) and four months (3rd) later only in those subjects who had negative results at the baseline in both the IFN-gamma assays and TST. An induration size > 10 mm was considered to be positive in the TST. RESULTS: The mean TST value was 3.1 +/- 5.4 mm (range: 0-20). Of the 46 subjects examined, 13 subjects (28.3%) showed positive results in the two-step TST. Nine (19.6%) were SPOT-positive and only one (2.2%) was QFT-positive. The 2nd and 3rd QFT were carried out in 23 and 25 all-negative subjects, respectively, and all showed negative results. The 2nd SPOT was performed in 23 subjects and only one (4.3%) showed a weak-positive result. CONCLUSION: Even though there were some discrepancies in the results of the two ex-vivo IFN-gamma assays, it appears that their results were not influenced by a previous TST carried out in two or four months earlier.

Key Words: Latent tuberculosis infection, Interferon-gamma assay, Tuberculin skin test, Purified Protein Derivative