CORRELATING QUALITATIVE/QUANTITATIVE QUANTIFERON-TB GOLD PLUS RESULTS AND CD4+ COUNT: A RETROSPECTIVE STUDY IN A HIV COHORT

Tuberculosis is the worldwide leading cause of morbidity and mortality in HIV+ people. Current CDC guidelines for the detection of Mycobacterium tuberculosis infection state that TSTs and IGRAs (QFT-G, QFT-GIT, and T-Spot) should be used as screening tests for TB infection in all HIV+ individuals. From 2007 QuantiFERON-TB Gold in Tube (QFT-GIT) was the most widely used test in high resources settings until when, in 2016, QuantiFERON-TB Gold Plus was approved by the Food and Drug Administration (FDA). The difference in the new version is mainly the presence of an additional test tube (TB2), which is designed to elicit and quantify the response of CD8+ T cells in addition to that of CD4+ T cells. The implementation of TB2 should provide a more precise assessment of the individual’s immune response to tubercular antigens compared to QFT-GIT. In order to study the actual efficacy of this new tool, we retrospectively collected a large and diverse sample of HIV+ patients that had at least 1 QuantiFERON-TB Gold Plus test done in a high resources, low TB incidence country. What we found was a substantial improvement of the test efficacy with respect to the previous QFT-GIT version. In the first place we observed a much lower percentage (1,2%) of indeterminate results ascribable to technical and procedural advancement. On the contrary to QFT-GIT, in QFT-Plus we didn’t find correlations between the CD4+ count and the quantitative and qualitative results of the test. Moreover, we found a possible correlation between the TB1 sample result and the stage of TB progression in the positive tests. Lastly, we couldn’t find any association between patients’ characteristics and reversion of the QFT after active TB treatment.