Figure 4.

Flow cytometry (FC) test measurements and combination of immunodiagnostic tests distinguish between unexposed subjects, untreated patients with latent tuberculosis infection (LTBI), and treated patients with LTBI. (A) Bivariate normal density ellipse with 95% coverage for QuantiFERON TB Gold In-Tube (QFT)(+) results (red color) and QFT(−) results (blue color) and correspondent FC test results: percentage of CD25⁺CD134⁺ of CD3⁺CD4⁺ T cells (region of difference 1 [RD1] peptide antigen [Ag] − negative control [nil]) versus percentage of CD25⁺CD134⁺ of CD3⁺CD8⁺ T cells (purified protein derivative [PPD] − nil) by study groups. The cut-offs for the FC tests were those associated with the highest specificity to separate treated from untreated LTBI cases (dashed lines, optimized FC test cut-offs). (B) Pie charts represent the number of subjects with positive or negative immunodiagnostic test results (using the optimized FC test cut-offs) by study groups. FC assay CD4⁺ (RD1 Ag − nil) = FC assay for the percentage of CD25⁺CD134⁺ of CD3⁺CD4⁺ T cells (RD1 Ag − nil); FC assay CD8⁺ (PPD − nil) = FC assay for the percentage of CD25⁺CD134⁺ of CD3⁺CD8⁺ T cells (PPD − nil).