Consideration of Improvement Measures from Limitations of Immunological Tests― including Interferon-γ Release and Antibody-based Detection Assays―for Mycobacterium Tuberculosis Infection

Purpose] Mycobacterium tuberculosis (MTB) infection should be detected in all patients before progressing to active tuberculosis (TB) ; however, interferon-γ release assays (IGRAs) and serological assays cannot accurately detect TB infection in all patients. Therefore, we conducted a prospective study to determine whether TB infections in patients with active pulmonary TB could be reliably detected by combined use of both tests. [Methods] We consecutively enrolled 186 patients suspected of having pulmonary TB referred to our institute between October 2008 and March 2010 in this study. All patients underwent IGRA and serological assays at fi rst visit and subjected for differential diagnoses. [Results] MTB infections could be detected in 49 of 50 patients with active pulmonary TB using tests of humoral and cellular immune responses. However, falsepositive serological tests and IGRAs using TB-specifi c antigens were observed in patients with nontuberculous Mycobacterium (NTM), old TB, or other respiratory diseases. [Conclusion] MTB infections were detected in nearly all patients with active pulmonary TB using tests of humoral and cellular immune responses. However, these assays need to be improved in order to differentiate the active MTB infection from latent MTB infection or NTM infection using combined other separate antigens.