[Comparison of two interferon-gamma release assays in the diagnosis of tuberculosis]

To compare the diagnostic performance of A.TB, an ELISA-based interferon-gamma release assay (IGRA), and T-SPOT.TB, an ELISPOT-based IGRA, and therefore to evaluate the value of A.TB assay in the routine clinical practice.

From March to May of the year of 2011, 112 hospitalized patients were enrolled from 2 chest hospitals in Beijing and Harbin, including 75 cases in the TB group (43 male and 32 female) with the average age of (44 ± 18) years, spanning from 28 to 57 years, and 37 cases in the non-TB group (21 male and 16 female) with the average age of (54 ± 10) years, spanning from 24 to 82 years. During the same period, 34 healthy volunteers (4 male and 30 female), with the average age of (20 ± 0.6) years, spanning from 19 to 22 years, were recruited in Beijing Chest Hospital. A head-to-head comparison of the 2 IGRAs was performed on the 146 subjects to evaluate their overall diagnostic performance. Chi-square test or Fisher's exact test was used for statistical analysis of enumeration data.

The sensitivity and specificity of A.TB were 81.3% (61/75, 95%CI = 72.5 - 90.2) and 83.1% (59/71, 95%CI = 74.4 - 91.8) respectively, compared to 90.7% (68/75, 95%CI = 84.1 - 97.3) and 78.9% (56/71, 95%CI = 69.4 - 88.4) for T-SPOT.TB. There was no significant difference in sensitivity or specificity (chi square values were 2.77 and 0.17 respectively, both P > 0.05). The area under the ROC curve was 0.90 (95%CI = 0.84 - 0.95) for A.TB and 0.91 (95%CI = 0.86 - 0.96) for T-SPOT.TB. The observation agreement between the 2 methods was 87.2% (123/141), with a kappa value of 0.74. T-SPOT.TB produced indeterminate results at a rate of 3.4% (5/146).

There was comparable diagnostic performance between the 2 assays. However, when compared to T-SPOT.TB, the A.TB testing procedure, with less technical demand and without requirement of well-equipped lab, is simpler and the interpretation of results is less subjective.