Table 3.
Variability in semiquantitative results around manufacturer-defined cut-point: results for QuantiFERON-TB Gold In-Tube assay
| Variable Assessed | No. of Studies (Total No. of Samples) | Baseline Tuberculosis-Specific IFN-γ
(IU/ml) |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0–0.1 |
0.11–0.24 |
0.25–0.34 |
0.35–0.8 |
0.81–1.49 |
1.5–2.9 |
3–4.99 |
5–6.99 |
7–10 |
||
| % Conversions (Total N) | % Reversions (Total N) | |||||||||
| Retesting under identical conditions | 5 (739) | 2 (255) | 6 (73) | 26 (55) | 18 (94) | 2 (62) | 7 (63) | 0 (27) | 0 (16) | 0 (94) |
| Repeat testing within 4 wk | 8 (1,061) | 2 (205) | 10 (31) | 14 (7) | 57 (420) | 40 (158) | 34 (106) | 23.3 (43) | 33.3 (27) | 14 (64) |
| | ||||||||||
| Repeat ELISA within 2 h | 1 (114) | 0 (72) | 0 (12) | — | 0 (18) | 0 (6) | 0 (6) | — | — | — |
| Incubation delay | |
|||||||||
| 12 h vs. immediate | 2 (168) | 2 (122) | 0 (8) | 33(3) | 67 (6) | 38 (8) | 33 (6) | 20 (5) | 0 (1) | 0 (9) |
| 6 h vs. immediate | 2 (148) | 1(106) | 0 (8) | 33(3) | 50 (6) | 38 (8) | 25 (4) | 20 (5) | 0 (1) | 0 (7) |
| Interoperator variability | 2 (42) | 0 (21) | 0 (4) | — | 0 (2) | 25 (4) | 0 (2) | 0 (1) | 0 (1) | 0 (7) |
| Plasma storage | |
|||||||||
| 4°C vs. 0°C | 1 (288) | 0 (155) | 0 (13) | 0 (2) | 36 (72) | 27 (22) | 15 (13) | — | 0 (5) | 0 (6) |
| −80°C vs. 0°C | 1 (21) | 0 (6) | 0 (3) | — | 0 (2) | 25 (4) | 0 (1) | — | 0 (1) | 0 (4) |
| Boosting by negative skin test | 5 (219) | 4(193) | 10 (10) | 33 (3) | 43 (7) | 20 (5) | 0 (1) | — | — | — |