Utility of QuantiFERON-TB In-Tube Test for Differentiating Active Tuberculosis from Latent Tuberculosis Infection in an Intermediate Burden Country

Background : The aim of the present study was to assess the contribution of a QuantiFERON-TB Gold In-Tube test (QFT-IT) in differentiating active tuberculosis (TB) from latent tuberculosis infection (LTBI) by quantifying interferon-gamma levels. Materials and Methods : We retrospectively reviewed clinical records of 314 patients older than 15 years who had performed QFT-IT between July 2006 and August 2007 at a tertiary care teaching hospital. Results : Subjects with active TB (n=81, culture confirmed active TB in 40 subjects) and LTBI (n=76) were included. Mean +/- SD IFN-gamma levels were 4.96 +/- 3.98 IU/mL (range -0.08-10) for all subjects with active TB, 4.54 +/- 4.05 IU/mL (range -0.08-10) for culture confirmed active TB, and 4.11 +/- 3.57 IU/mL (range 0.35-10) for subjects with LTBI. The quantitative results of QFT-IT on IFN gamma levels between all the subjects with active TB and those with LTBI were not statistically significant (P= 0.16). The result was similar when compared between those with culture confirmed active TB and those with LTBI, showing little statistical significance (P= 0.554). Conclusion : The production of IFN-gamma measured by QFT-IT showed no correlation between its level and the activity of Mycobacterium tuberculosis infection. These results suggest that measuring IFN-gamma using QFT-IT might not be useful for distinguishing active TB from LTBI.