Table 4 Comparison of T cell-based tests for TB infection
From: Tuberculosis exposure, infection and disease in children: a systematic diagnostic approach
Characteristic | Tuberculin Skin Test | QuantiFERON-TB®* | T-SPOT-TB®** |
|---|---|---|---|
Time to results | 48–72 h | 24–36 h | 36–48 h |
Complexity | Low | Moderate | High |
TB antigens | PPD-tuberculin (not specific to M. tb.) | ESAT-6; CFP-10; TB-7.7 | ESAT-6; CFP-10 |
Measurement | Skin induration after in vivo stimulation | ELISA-based measurement of IFN-γ production by T-cells after in vitro stimulation | ELISPOT-based measurement of IFN-γ-producing T-cells (spots) after in vitro stimulation |
Minimum number of visits to complete testing | 2 visits (within 48–72 h of placement) | 1 visit | |
Sample/Method | Intradermal injection of 5 units of PPD-tuberculin | Blood draw | |
Reliability/Variability of test results | Limited variability with appropriate training [34] | ||
Cross-reactivity with BCG vaccine | Yes (particularly if vaccinated after infancy or repeatedly) [37, 38] | No | |
NTM cross reaction | Many | Few (M. kansasii, M. marinum, M. szulgaii) | |
Booster effect with repeated testing | Yes | No | |
Booster effect after prior TST | Yes | Possible (but likely inconsequential if blood drawn < 3 days after TST [39] | |
Internal controls | No | Yes | |
Utility by age | Less reliable in children under 6-months of age | Less reliable in children under 5-years of age | |
Sensitivity with bacteriologically-confirmed TB | 75–85% [40] | 80–85% [40] | |
Specificity with bacteriologically-confirmed TB | 95–100% [40] With BCG vaccination 49–65% [40] | 90–95% [40] With BCG vaccination 89–100% [40] | |
Sensitivity in HIV-infected patients | 45% [36] | Same as TST [36]; T-SPOT.TB slightly less affected by immunosuppression than QFT [41] | |