[Evaluation of a commercial enzyme immunoassay for the detection of interferon gamma levels in active tuberculosis patients and vaccinated healthy subjects].

The detection of plasma interferon gamma (IFN-g) levels has an important value for the evaluation of cell mediated immune response to Mycobacterium tuberculosis. The aim of this study was to investigate the plasma IFN-g levels by a commercial enzyme immunoassay (ELISA) and to compare the levels between recently diagnosed culture positive lung tuberculosis patients and BCG vaccinated healthy controls. Twenty-three patients with active lung tuberculosis (13 males, 10 females) and 34 BCG vaccinated healthy adults (16 male, 18 female) have been included in the study. The control subjects were questioned about passed tuberculosis infection and/or a contact with tuberculosis patients. No risk factors for exposure to M. tuberculosis were found in the control group. IFN-g levels were measured by QuantiFERON-TB (Cellestis, Australia) kit, and 22 of patients and 17 of control subjects were found to be positive. As a result, the sensitivity of QuantiFERON-TB test was high (95.6%), however its specificity was quite low (50%). In conclusion, QuantiFERON-TB may be used as a supplementary diagnostic test in patients considered to have active tuberculosis, before treatment. As BCG is in routine vaccination programme and the number of active tuberculosis cases is high in our country, this test seems to be invalid for the diagnosis of latent tuberculosis. Therefore, more specific tests that are not affected by the vaccine response, are required for the diagnosis of latent tuberculosis.