Yields for test positivity by different screening tests at different screening thresholds
| TB incidence screening threshold (/100 000 per year) | No. tested | No. positive | Yield at incidence level, that is, proportion of those tested | Positives identified if threshold set at this level (%) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TST | QFN | TSPOT | TST | QFN | TSPOT | TST | QFN | TSPOT | TST | QFN | TSPOT | |
| Screen ≥350 | 4 | 11 | 4 | 1 | 1 | 1 | 25.0 | 9.1 | 25.0 | 1.9 | 2.6 | 2.8 |
| Screen ≥300 | 5 | 13 | 6 | 1 | 2 | 3 | 20.0 | 15.4 | 50.0 | 1.9 | 5.3 | 8.3 |
| Screen ≥250 | 23 | 37 | 28 | 10 | 13 | 12 | 43.5 | 35.1 | 42.9 | 18.9 | 34.2 | 33.3 |
| Screen ≥200 | 50 | 75 | 59 | 20 | 19 | 17 | 40.0 | 25.3 | 28.8 | 37.7 | 50.0 | 47.2 |
| Screen ≥150 | 71 | 105 | 84 | 26 | 27 | 25 | 36.6 | 25.7 | 29.8 | 49.1 | 71.1 | 69.4 |
| Screen ≥100 | 104 | 143 | 110 | 30 | 29 | 28 | 28.9 | 20.3 | 25.5 | 56.6 | 76.3 | 77.8 |
| Screen ≥40 * | 170 | 222 | 158 | 52 | 38 | 36 | 30.6 | 17.1 | 22.8 | 98.1 | 100.0 | 100.0 |
| Screen all | 175 | 229 | 160 | 53 | 38 | 36 | 30.3 | 16.6 | 22.5 | 100.0 | 100.0 | 100.0 |
↵* Current threshold recommended by National Institute for Health and Clinical Excellence guidance is given in bold text.
QFN, QuantiFERON Gold in-tube; TB, tuberculosis; TST, tuberculin skin test.