Abstract
Objective: The specificity of IGRAs with the population being tested. The specificity of T-SPOT®.TB (T-SPOT) is generally reported to be lower than that of QuantiFERON®-TB Gold In-Tube (QFT-GIT). It is likely that studies carried out in developing countries include individuals with latent tuberculosis infection (LTBI). Therefore, we compared the specificities of T-SPOT and QFT-GIT in selected healthy subjects in Japan.
Subjects and methods: Blood samples were taken for both T-SPOT and QFT-GIT from university students who were selected according to stringent inclusion criteria and performed according to the manufacturer's instructions. Blood samples for T-SPOT were kept overnight at room temperature and treated the next day with T-Cell Xtend before PBMCs preparation. Blood samples for QFT-GIT were incubated within 16 hours after blood collection.
Results: University students with very low risk factors for TB infection were selected for the study. Of 111subgects, one was positive in both assays and 110 were negative by T-SPOT and 96 were negative by QFT-GIT. No results were borderline by T-SPOT (between 5 and 7 spots, USA criteria) and 14 were borderline by QFT-GIT (between 0.1 and 0.35 IU/ml, Japanese criteria). There was no indeterminate result.
Conclusion: Although several meta-analyses showed that QFT-GIT has the higher specificity compared to T-SPOT, our result demonstrate that the specificity of both assays is equally high. This implies that subjects for specificity studies should be strictly selected, especially as there is no gold standard for LTBI. If studies do not meet these criteria, they should not be included meta-analyses.
- © 2011 ERS
