The Usefulness of the Tuberculosis Skin Test and the Interferon-gamma Release Assay in the Diagnosis of Latent Tuberculosis Infection in South Korea

OBJECTIVES South Koreans receive the bacillus Calmette-Guerin (BCG) vaccination, which influence the result of the tuberculin skin test (TST); however, only a few studies have described the usefulness of the TST and interferon-γ release assay (IGRA) for diagnosing latent TB infection (LTBI). Therefore, our aim was to determine the usefulness of the TST and IGRA for diagnosing LTBI in a household contacts investigation. METHODS We reviewed the 329 household contacts who visited Chung-Ang University Hospital (Seoul, Korea) from May 1, 2011 to February 28, 2014. To evaluate the effectiveness of TST and IGRA for the diagnosis of LTBI, we examined the concordance rate between the two tests, based on age. We also evaluated the risk factors for LTBI. RESULTS The concordance rate between the two tests in individuals 0-24 years, 25-54 years, and over 55 years were 82.6% (κ = 0.64, p < 0.01), 68.9% (κ = 0.40, p < 0.01), and 68.4% (κ = 0.35, p < 0.01), respectively. The ratio of positive TST to negative IGRA was higher in individuals 25-44 years old, whereas the ratio of negative TST to positive IGRA was higher in individuals older than 55 years old. Based on the TST, the risk factor for LTBI was a cavity (p < 0.01). When using IGRA, the risk factors were contact time (p = 0.04) and age over 55 years old (p = 0.02). CONCLUSION The concordance rate between TST and IGRA was not good after the age of 25 years. The IGRA test reflects the known risk factors more exactly.