# Table 1 Probabilities and cost-estimates used in the cost-analysis for screening of LTBI.

Variable Baseline Range Source
Probabilities
Prevalence of LTBI 0.30 0.1-0.4 [24, 39, 40]
TST return rate 0.90 0.65-0.95 [14, 27]
T-SPOT.TB sensitivity 0.95 0.83-0.97 [30, 4143]
T-SPOT.TB specificity 1.00 0.92-0.99 [41, 43]
T-SPOT.TB positive result 0.285   Calculated
T-SPOT.TB true positive (PPV) 1.000   Calculated
T-SPOT.TB true negative (NPV) 0.979   Calculated
T-SPOT.TB true positive (PPV) given a positive TST 1.000   Calculated
T-SPOT.TB negative (NPV) given a positive TST 0.987   Calculated
QFT-GIT sensitivity 0.89 0.85-0.95 [32, 44]
QFT-GIT specificity 0.95 0.90-0.97 [32, 44]
QFT-GIT positive result 0.302   Calculated
QFT-GIT true positive (PPV) 0.884   Calculated
QFT-GIT true negative (NPV) 0.953   Calculated
QFT-GIT true positive (PPV) given a positive TST 0.930   Calculated
QFT-GIT true negative (NPV) given a positive TST 0.971   Calculated
TST sensitivity 0.85 0.69-0.95 [30, 41, 42, 45]
TST specificity 0.80 0.65-0.90 [20, 46]
TST positive result 0.395   Calculated
TST true positive (PPV) 0.646   Calculated
TST true negative (NPV) 0.926   Calculated
Start INH treatment 0.80 0.55-0.95 [47]
Develop severe INH hepatitis 0.003 0.003-0.041 [4750]
Death due to hepatitis 0.00002 0.00001-0.0001 [51, 52]
Efficacy of 3 months INH (LTBI fully cured) 0.21 0.1-0.3 [23, 24, 53]
LTBI not cured (with 3 months INH) 0.79 0.7-0.9 [23, 24, 53]
Efficacy of 6 months INH (LTBI fully cured) 0.65 0.5-0.93 [10, 17, 23, 49, 53, 54]
LTBI not cured (with 6 months INH) 0.35 0.07-0.5 [10, 17, 23, 49, 53]
Post exposure TB 0.025 0.01-0.05 [14, 55]
TB remains latent 0.975 0.95-0.99 [14, 55]
Cost (British Pounds; £s)
T-SPOT.TB (kit, consumables and processing) + phlebotomy 55.00 45.00-100.00 Test cost from Royal Free Hospital, London; Phlebotomy cost from [56]