QTF-G positive test results according to different cutoffs for TST.
| TST Cut-off Values, mm | Agreement Between TST and QTF-G (%) | Kappa | p | |
|---|---|---|---|---|
| Rheumatoid arthritis | ≥ 5 | 54/77 (70) | 0.42 | NS |
| ≥ 10 | 57/77 (74) | 0.47 | NS | |
| ≥ 15 | 51/77 (71) | 0.35 | NS | |
| Ankylosing spondylitis | ≥ 5 | 27/55 (49) | 0.14 | NS |
| ≥ 10 | 32/55 (58) | 0.26 | 0.008 | |
| ≥ 15 | 42/55 (76) | 0.47 | < 0.001 |
QTF-G: Quantiferon-TB Gold test; TST: tuberculin skin test; NS: not significant.