Table 5. Variability in Quantiferon-TB Gold in-Tube test measurements performed on the same subjects in three labs excluding those with extremely high TB Response.
| LOA* | ||||||
| Measure | Comparison | n | Bias* † ± (SDD*) | W-S SD* (95%CI) | ICC (95% CI) | W-S CV% (95% CI) |
| Nil | ||||||
| Lab1 vs. Lab2 | ||||||
| Unstratified§ | 91 | 0.01±(0.11) | ±0.04 (0.03, 0.04) | 0.89 (0.84, 0.93) | 33.63 (29.38, 37.40) | |
| Concordant Positive# | 35 | 0.00±(0.12) | ±0.04 (0.04, 0.06) | 0.94 (0.89, 0.97) | 35.11 (28.53, 40.63) | |
| Concordant Negative∧ | 49 | 0.01±(0.10) | ±0.04 (0.03, 0.05) | 0.22 (−0.06, 0.47) | 33.56 (27.08, 38.98) | |
| Lab1 vs. Lab3 | ||||||
| Unstratified§ | 91 | −0.01±(0.16) | ±0.06 (0.05, 0.07) | 0.72 (0.61, 0.81) | 40.83 (35.50, 45.54) | |
| Concordant Positive# | 35 | −0.01±(0.17) | ±0.06 (0.05, 0.08) | 0.86 (0.74, 0.93) | 40.47 (30.89, 48.18) | |
| Concordant Negative∧ | 49 | −0.02±(0.16) | ±0.06 (0.05, 0.07) | 0.13 (−0.15, 0.39) | 41.91 (34.54, 48.16) | |
| Lab2 vs. Lab3 | ||||||
| Unstratified§ | 91 | −0.02±(0.19) | ±0.07 (0.06, 0.08) | 0.64 (0.50, 0.75) | 44.78 (38.78, 50.06) | |
| Concordant Positive# | 35 | −0.01±(0.22) | ±0.08 (0.06, 0.10) | 0.78 (0.61, 0.88) | 44.11 (36.00, 50.93) | |
| Concordant Negative∧ | 49 | −0.02±(0.17) | ±0.06 (0.05, 0.08) | −0.14 (−0.40, 0.14) | 46.54 (37.31, 54.21) | |
| TB | ||||||
| Lab1 vs. Lab2 | ||||||
| Unstratified§ | 91 | 0.19±(2.98) | ±1.08 (0.94, 1.26) | 0.97 (0.96, 0.98) | 28.23 (22.40, 33.05) | |
| Concordant Positive# | 35 | 0.48±(4.79) | ±1.73 (1.40, 2.27) | 0.96 (0.92, 0.98) | 23.14 (16.98, 27.97) | |
| Concordant Negative∧ | 49 | 0.00±(0.09) | ±0.03 (0.03, 0.04) | 0.69 (0.51, 0.81) | 26.07 (20.30, 30.77) | |
| Lab1 vs. Lab3 | ||||||
| Unstratified§ | 91 | 0.67±(6.18) | ±2.23 (1.95, 2.61) | 0.84 (0.77, 0.89) | 37.43 (32.06, 42.12) | |
| Concordant Positive# | 35 | 1.81±(9.62) | ±3.47 (2.81, 4.55) | 0.76 (0.58, 0.87) | 31.32 (25.36, 36.32) | |
| Concordant Negative∧ | 49 | −0.04±(0.19) | ±0.07 (0.06, 0.09) | 0.39 (0.13, 0.60) | 39.89 (31.87, 46.55) | |
| Lab2 vs. Lab3 | ||||||
| Unstratified§ | 91 | 0.48±(4.28) | ±1.54 (1.35, 1.81) | 0.91 (0.87, 0.94) | 35.37 (29.77, 40.19) | |
| Concordant Positive# | 35 | 1.33±(6.61) | ±2.38 (1.93, 3.12) | 0.85 (0.73, 0.92) | 26.99 (19.91, 32.57) | |
| Concordant Negative∧ | 49 | −0.05±(0.20) | ±0.07 (0.06, 0.09) | 0.32 (0.05, 0.55) | 40.57 (32.31, 47.42) | |
| TB Response | ||||||
| Lab1 vs. Lab2 | ||||||
| Unstratified§ | 91 | 0.19±(2.97) | ±1.07 (0.94, 1.26) | 0.97 (0.96, 0.98) | 43.91 (36.95, 49.91) | |
| Concordant Positive# | 35 | 0.48±(4.77) | ±1.72 (1.39, 2.26) | 0.96 (0.92, 0.98) | 42.04 (33.20, 49.32) | |
| Concordant Negative∧ | 49 | 0.00±(0.08) | ±0.03 (0.03, 0.04) | 0.70 (0.53–0.82) | 42.49 (33.84, 49.66) | |
| Lab1 vs. Lab3 | ||||||
| Unstratified§ | 91 | 0.68±(6.17) | ±2.23 (1.94, 2.61) | 0.84 (0.77, 0.89) | 55.39 (47.83, 62.03) | |
| Concordant Positive# | 35 | 1.82±(9.61) | ±3.47 (2.80, 4.54) | 0.76 (0.58, 0.87) | 51.17 (39.96, 60.33) | |
| Concordant Negative∧ | 49 | −0.03±(0.11) | ±0.04 (0.03, 0.05) | 0.56 (0.34, 0.72) | 57.86 (47.00, 66.98) | |
| Lab2 vs. Lab3 | ||||||
| Unstratified§ | 91 | 0.50±(4.29) | ±1.55 (1.35, 1.81) | 0.91 (0.87, 0.94) | 57.06 (48.89, 64.20) | |
| Concordant Positive# | 35 | 1.35±(6.64) | ±2.40 (1.94, 3.14) | 0.85 (0.73, 0.92) | 51.71 (41.14, 60.46) | |
| Concordant Negative∧ | 49 | −0.03±(0.11) | ±0.04 (0.03, 0.05) | 0.63 (0.43, 0.77) | 61.74 (49.35, 72.03) |
*
LOA, bias, SDD, and W-S SD are in IU/mL of IFN-γ.
†
Directionality for bias and LOA comparisons: Lab1-Lab2, Lab1-Lab3, Lab2-Lab3.
§
Includes 7 subjects with discordant QFT-GIT interpretations.
#
Concordant positive among results from all 3 labs.
∧
Concordant negative among results from all 3 labs.