Table 2 Interferon γ assay and the tuberculin skin test according to the presence of absence of risk factors for latent Mycobacterium tuberculosis infection and BCG vaccination
CharacteristicInterferon γ assay (IFNγ)Tuberculin skin test (TST)IFNγ vs TST
Odds ratio (95% CI)p ValueOdds ratio (95% CI)p Valuep Value
Univariable analysis
Presence of risk factor23.8 (5.14 to 110)<0.0012.77 (1.22 to 6.27)0.0150.009
BCG vaccination0.47 (0.15 to 1.47)0.202.44 (0.74 to 8.01)0.140.025
Multivariable analysis
Presence of risk factor29.2 (5.91 to 144)<0.0014.81 (1.80 to 12.8)0.0020.041
BCG vaccination1.79 (0.49 to 6.50)0.375.83 (1.46 to 23.3)0.0130.20
  • Association between the presence of any risk factor for latent tuberculosis or BCG vaccination status and results of IFNγ assay (n = 134) and TST (n = 115) from univariable analysis and multivariable analysis including both the presence of risk factors and BCG vaccination as independent variables. An odds ratio of 23.8 indicates, for example, that patients with a risk factor for latent tuberculosis have an odds for a positive IFNγ assay, which is 23.8 times higher than the odds of patients without a risk factor. The p value for differences in performance between IFNγ assay and TST is from matched-pairs logistic regression analysis. Refer to fig 2 for numbers of patients with positive test results according to risk factor and BCG vaccination status.