Utility of an interferon-gamma release assay as a potential diagnostic aid for active pulmonary tuberculosis

Abstract

Introduction: Sensitivity, specificity, early confirmation and obtaining an optimal specimen are challenging problems in active tuberculosis (TB) diagnosis. Interferon-gamma release assay (IGRA) is a good indicator for latent TB but can it be useful as a diagnostic tool for active TB? This study was designed to address these challenges and assess the potential of IGRA as a diagnostic indicator of active pulmonary TB by comparing it with other MT diagnostic conventional methods and molecular methods. Methodology: The study was conducted on 91 patients with suspicion of pulmonary active TB. QuantiFERON-TB-Gold In-Tube, a commercial IFN-gamma assay, was compared with Ziehl Neelsen (ZN) smear, Lowenstein Jensen's (LJ) egg-based culture, and real-time polymerase chain reaction. The final clinical diagnosis was the standard comparator of the study. Results: Active pulmonary TB was confirmed in 48/91 (52.7%) patients. Sensitivity, specificity, positive predicted value (PPV), and negative predicted value (NPV) were 72.9%, 100%, 100%, 76.78% for ZN smear, 77.1%, 97.67%, 97.36%, 79.24% for LJ culture, 89.9%, 67.4%, 75.4%, 85.3% for IGRA, and 66.6%, 95.3%, 94.1%, 71.9% for real-time PCR, respectively. Conclusion: Albeit confounding in the case of latent TB infected patients presenting with non-TB pulmonary disease, IGRA was more sensitive than the other conventional and molecular methods, so it may improve diagnostic accuracy when used in combination with other standard methods. High NPV of IGRA for the diagnosis of active TB proposed an additional role of this test to exclude the infection with active TB.

Cost-effectiveness in the diagnosis of tuberculosis: choices in developing countries

“…The performance of IGRAs has been examined in numerous studies of immunocompetent subjects, HIV-infected individuals, and children. Overall, the data in the literature indicates that both IGRAs have a better specificity and correlation with exposure to MTB than the TST and equal or greater sensitivity [4]. The greater specificity of IGRAs in comparison to the TST is very important for the correct identification of infected subjects and for the administration of preventive therapy.…”

Tuberculin skin test and QuantiFERON-Gold In Tube assay for diagnosis of latent TB infection among household contacts of pulmonary TB patients in high TB burden setting

“…Unlike these reports, a recently published systematic review using latent class modelling to assess the utility of TST and QFT-GIT for LTBI diagnosis in different population groups showed a low sensitivity (52%) but high specificity (97%) of QFT-GIT to diagnose LTBI [ 28 ]. Even active TB studies have reported low sensitivity but varying specificity for QFT-GIT [ 29 , 30 ]. Furthermore, as the strength of TST product is increased, the induration cut-off for a positive TST gets reduced and is closer to positivity of QFT-GIT.…”

Untitled

“…1,15 On the other hand, the specificity of IGRA has been between 67.4% to 98.1% in the immunocompetent population. 16,17 Only 5% of evaluated patients had a positive TST, despite prior BCG vaccination in all of our subjects during childhood, which might potentially lead to false-positive TST results. Our data are low compared with previous reports that show a 24% positive outcome.…”