Table 3

Performance outcomes (95% CI) of IRGAs (T-SPOT.TB, QFT-GIT) using alveolar lavage cells and whole blood, at different cut-off points, in patients suspected of having pulmonary TB (definite TB (n = 24) and non-TB groups (n = 48) used in the analysis).

Cut-off pointSensitivitySpecificityPPVNPVAccuracyAUC
Alveolar lavage cells
T-SPOT.TB (combined RD-1 antigen)⩾30 SFC*78% (55–91)94% (80–98)89% (64–97)88% (74–95)88% (76–94)n/a
⩾50 SFC†72% (49–88)97% (84–99)93% (69–99)86% (72;94)88% (76–94)
⩾20 SFC‡88% (67–97)94% (80–98)89% (67–97)94% (80–98)92% (81–97)
T-SPOT.TB⩾30 SFC*78% (55–91)94% (80–98)88% (64–97)88% (74–95)88% (76–94)0.96
ESAT-6⩾50 SFC†72% (49–88)97% (84–99)93% (69–99)86% (71–94)88% (76–94)
⩾20 SFC‡89% (67–97)91% (76–97)84% (62–94)94% (79–98)90% (78–96)
T-SPOT.TB⩾30 SFC*67% (44–84)94% (80–98)86% (60–96)83% (68–92)84% (71–92)0.84
CFP-10⩾70 SFC†61% (39–80)97% (84–99)92% (65–99)82% (67–91)84% (71–92)
QFT-GIT>0.35 IU/ml*55% (34–75)86% (65–95)77% (5–92)69% (50–84)72% (56–83)0.77
>0.045 IU/ml†83% (61–94)76% (55–89)75% (53–89)84% (62–95)79% (64–89)
>6.2 IU/ml‡28% (13–51)95% (77–99)83% (44–97)61% (44–75)64% (48–77)
Peripheral whole blood
T-SPOT.TB⩾30 SFC*100% (83–100)45% (31–60)45% (31–60)100% (83–100)62% (50–73)n/a
QFT-GIT>0.35 IU/ml*68% (46–85)54% (36–71)52% (34–70)70% (48–86)60% (46–73)0.71
  • Forty T-SPOT.TB (SFCs per 106 alveolar mononuclear cells) and 39 QFT-GIT (IU/ml) assays were performed.

  • The results reflecting outcomes when the definite and probable groups are combined are shown in the online data supplement.

  • *Manufacturer-recommended cut-off point for peripheral blood of >20 SFCs per million mononuclear cells in either the ESAT-6- or CFP-10-containing wells

  • †AUC-derived cut-off point with a high specificity at the expense of sensitivity.

  • ‡AUC-derived cut-off point with the best possible specificity at a high sensitivity.

  • AUC, area under the curve; IRGA, interferon γ release assay; n/a, not applicable (this is a dichotomised variable and hence the AUC cannot be calculated); NPV, negative predictive value; PPV, positive predictive value; QFT-GIT, QuantiFERON-TB Gold-In-Tube; SFC, spot-forming cell; TB, tuberculosis.