A comparative analysis of two interferon-γ releasing assays to detect past tuberculosis infections in Japanese rheumatoid arthritis patients.

OBJECTIVES: To compare the utility of QuantiFERON-TB Gold in tube (QFT-GIT) and T-SPOT.TB assays to detect past tuberculosis infection in Japanese rheumatoid arthritis patients receiving methotrexate. METHODS: We compared the sensitivities and specificities, the rates of indeterminate results, and the rates of positive results in patients with total and CD4-positive lymphocyte counts of both assays simultaneously performed on 68 rheumatoid arthritis patients receiving methotrexate, in whom 33 had evidence of past tuberculosis infection by chest computed tomography and the other had neither history of tuberculosis exposure nor abnormalities in chest computed tomography. RESULTS: The sensitivities, specificities, and the rates of indeterminate results of QFT-GIT were 21.2%, 100%, and 4.4%, and those of T-SPOT.TB were 21.9%, 100%, and 1.5%, respectively. The overall agreement of both assays was good (κ = 0.68). In patients with past tuberculosis infection, there are significant positive linear trends in positive rates of both assays across ranges of larger numbers of total and CD4-positive lymphocyte counts. CONCLUSIONS: Both assays were equally useful with high specificities, but may falsely identify past tuberculosis infection owing to low sensitivities. In patients with low total and CD4-positive lymphocyte counts, both assays might give higher rates of false negative results.