Objectives: The risk of activation of latent tuberculosis infection (LTBI) is increased in patients treated with anti-TNF-α drugs. Tuberculin skin test (TST) and Quantiferon-TB Gold test (QFT) are used to detect LTBI before and during anti-TNF-α treatment. We describe here a relation of these tests at various timepoints and also longitudinal QFT data.
Methods: Study group consisted of 305 patients with several rheumatic inflammatory diseases treated and/or scheduled for anti-TNF-α drugs. The QFT was performed in 303 patients during therapy and in 177 patients also during screening. The TST was used in 284 patients. Both tests simultaneously were utilised in 360 instances.
Results: Twenty-two patients were QFT positive; 3.9% before and 5.9% during anti-TNF-α treatment. Two patients who became QFT positive developed active tuberculosis. The TST was positive in 42% and 38% of patients before and during treatment, respectively. There was poor agreement between the two tests. Patients on glucocorticoids had a negative TST more frequently. The IFN-γ response to mycobacterial antigens significantly increased after application of tuberculin, but never reached the positive threshold. There was a significant increase in mitogen-induced IFN-γ production after initiation of anti-TNF-α therapy.
Conclusions: Poor correlation between the QFT and TST renders the TST non-specific for LTBI. QFT is more specific to detect LTBI and conversion to a positive result may predict active TB. An increase in IFN-γ production in response to mycobacterial antigens is seen when the TST is performed before the QFT. Mitogen-induced IFN-γ production increases after initiation of anti-TNF-α therapy.