Table 3 Increase in odds for a positive test for individual risk factors
CharacteristicInterferon γ assay (IFNγ)Tuberculin skin testing (TST)
ResultOdds ratio (95% CI)p Value for trendResultOdds ratio (95% CI)p Value for trend
PositiveNegativePositiveNegative
No risk factors (reference)2891.00 (0.14 to 7.26)<0.00126541.00 (0.52 to 1.94)0.13
Born or resident in high-prevalence country51911.7 (2.11 to 65.0)1173.26 (1.13 to 9.39)
History of household contact2517.8 (2.06 to 154)626.23 (1.18 to 33.01)
Chest x ray suggestive of a history of tuberculosis6466.8 (10.1 to 441)250.83 (0.15 to 4.57)
History of active tuberculosis20179 (6.69 to 4787)112.08 (0.12 to 34.53)
  • Association between individual risk factors for latent tuberculosis and results of IFNγ assay (n = 134) and tuberculin skin test (n = 115). Risk factors were ranked a priori according to their prognostic relevance from least to most relevant. A person who had multiple risk factors was included in the stratum of the most relevant risk factor. Odds ratios were calculated using patients without risk factors as reference group; p values are from tests for trend across ordered groups. An odds ratio of 17.8 indicates, for example, that the odds for a positive IFNγ assay is 17.8 times higher in patients with a history of household tuberculosis contact than in patients without a risk factor. The p value from matched-pairs logistic regression for differences in performance between IFNγ assay and TST across ordered groups was p<0.001.