Comparison of T-Spot.TB and tuberculin skin test among silicotic patients

In the present study, T-Spot.TB and the tuberculin skin test (TST) were compared in the screening of latent tuberculosis infection among silicotic patients. A conditional probability model was used to compare the potential clinical utilities of T-Spot.TB and TST performed on 134 silicotic subjects from December 1, 2004 to January 31, 2007. Data from a historical cohort were also reanalysed for further comparison. Agreement with T-Spot.TB was best using a TST cut-off of 10 mm. Age >= 65 yrs independently predicted a tuberculin reaction <10 mm (odds ratio=3), but not a negative T-Spot.TB response. Lower measures of agreement were observed among current smokers and those aged >= 65 yrs. Tuberculin reaction size was well correlated with both early secretary antigenic target 6 and culture filtrate protein 10 spot counts, except among current smokers. Within the current estimates of sensitivity (88-95%) and specificity (86-99%) for T-Spot.TB, the positive likelihood ratio for T-Spot.TB test would be substantially higher (6.29-95.0 versus 1.65-1.94) and negative likelihood ratio substantially lower (0.05-0.14 versus 0.32-0.41) than the corresponding ratios for the tuberculin test. A low tuberculosis risk differential was similarly observed between tuberculin-negative and untreated tuberculin-positive subjects in the historical cohort. T-Spot.TB is likely to perform better than tuberculin test in the screening of latent tuberculosis infection among silicotic subjects.