Application of IFN-γ/IL-2 FluoroSpot assay for distinguishing active tuberculosis from non-active tuberculosis: A cohort study

Currently available Interferon-γ release assay cannot reliably differentiate active TB (ATB) from non-active TB (non-ATB). This study aimed to evaluate the diagnostic accuracy of the IFN-γ/IL-2 FluoroSpot assay, which can simultaneously detect IFN-γ and IL-2 secretion, for differentiating ATB from non-ATB. 191 suspected ATB patients with positive T-SPOT.TB results were consecutively recruited. 64 (33.5%) participants had ATB, including 22 (34.4%) microbiologically or histologically confirmed TB and 42 (65.6%) clinically diagnosed TB. 119 (62.3%) cases were non-ATB and 8 (4.2%) were clinically indeterminate. After being stimulated with ESAT-6 and CFP-10 antigens, the median frequency and proportion of IFN-γ + IL-2 - T cells were significantly higher in the ATB group than the non-ATB group (P + IL-2 - T cells were larger than those of total IFN-γ + T cells (0.788 vs. 0.739, p = .323). With a cutoff value of 25 SFCs/250,000 PBMCs for frequency, sensitivity and specificity of this assay were 73.4% and 69.8% respectively. When combining the frequency and proportions of IFN-γ + IL-2 - T cells, the sensitivity and specificity were increased to 95.3% in parallel testing and 83.2% in serial testing respectively. In conclusion, IFN-γ/IL-2 FluoroSpot assay is conducive for the diagnosis of ATB in patients with positive T-SPOT.TB results.