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

¹ Tuberculosis and Chest Service, Centre for Health Protection, Dept of Health, ² Dept of Microbiology and Centre of Infection, University of Hong Kong, and ³ Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, China.

CORRESPONDENCE: C. C. Leung, Pneumoconiosis Clinic, 4/F, 8 Chai Wan Road, Shaukeiwan, Hong Kong, China. Fax: 86 85229775940. E-mail: cc_leung{at}dh.gov.hk

Keywords: Latent tuberculosis infection, silicosis, smoking

Received: May 7, 2007
Accepted October 12, 2007

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.

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