The reactivation of previous tuberculosis (TB) infection has become a serious complication of the biological treatment of patients with rheumatoid arthritis (RA) [1]. This study compared the results of two tests for latent tuberculosis infection—an interferon (IFN)-γ release assay [the QuantiFERON-TB Gold test (QFT), Cellestis, Carnegie, Australia] and the tuberculin skin test (TST)—in Japanese patients with RA in whom the history of previous TB infection was assessed with computed tomography (CT) of the chest. The rate for positive results for the QFT was significantly higher in patients with a history of TB infection and significantly lower in patients without infection. Furthermore, the mean diameter of induration with the TST was less in patients with previous TB infection than in patients without infection. Under Japanese guidelines for the treatment of RA, the history of previous TB infection must be assessed by means of interview, the TST, and chest radiography before the administration of biological agents [2]. To avoid unnecessary administration of prophylactic medication, it is recommended that patients with a history of previous TB infection be accurately identified.

Examinations for tuberculosis infection are performed for healthcare workers who come in contact with patients with sputum smears positive for TB [3]. The Japanese Society for Tuberculosis recommends that the QFT be used to diagnose tuberculosis infection, and most hospitals use the QFT instead of the TST [4]. Because the QFT does not affect subsequent Bacille Calmette-Guérin vaccination, it is convenient for detecting latent tuberculosis infection [5]. The QFT has high specificity for cross-contact infection but low sensitivity when the cutoff value for the IFN-γ titer is 0.35 IU/ml; therefore, in case of a high QFT positive rate, we use an IFN-γ titer of at least 0.1 IU/ml when deciding to administer prophylactic medication [4].

In the present study, the TST was considered unreliable for determining a history of past TB infection in patients with RA. Chemoprophylaxis with isoniazid is performed for patients with positive TST results (induration ≥20 mm). It is important to prevent overuse, because isoniazid therapy can have severe side effects, such as liver damage [6]. It may necessary to perform the QFT for TST-positive patients and to set an IFN-γ cutoff value of 0.1 IU/ml [7]. A combination of the QFT, the TST, medical interview, and chest radiographic findings should be used to assess the history of TB infection [8].