© 2008 American Thoracic Society
Predictive Value of the Tuberculin Skin Test and the QuantiFERON-TB Gold In-Tube Assay for the Development of Active Tuberculosis DiseaseTo the Editor:In their article (1), Dr. Diel and colleagues reported the finding that in close contacts of active TB cases, a higher rate of progression to active TB was found among those who were QuantiFERON-TB Gold In-Tube assay (QFT) positive (14.6%) than the 2.3% progression rate found in those who were TST positive (P < 0.003). However, the authors did not show the statistical analysis in the sample restricted to the BCG-unvaccinated subjects, which found no difference between the tests: for QFT (whole sample of subjects with positive results) 6 of 41 or 14.6% and for TST (BCG-unvaccinated with positive result at 5-mm cutoff) 4 of 42 or 9.5% (P = 0.52 by Fisher's exact test). Even if the sample of QFT positives is restricted to those BCG-unvaccinated, the difference is not statistically significant either (QFT 5/23 vs. TST 4/42, P = 0.26). The study by Diel and coworkers (1) indicates that the TST predictive value is similar to QFT in the unvaccinated close contacts. Therefore, the TST should be the first option in the BCG-unvaccinated and, due to its cost and the inconvenience of venipuncture, the use of QFT should be restricted to the BCG-vaccinated. Even though the TST has not been considered the gold standard for LTBI, its use in clinical practice continues; it is almost always considered the comparison group in IGRA research studies, and it is currently the most used screening tool.
British Columbia Centre for Disease Control FOOTNOTES Conflict of Interest Statement: The author has no financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
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assay for the development of active tuberculosis disease after recent infection with Mycobacterium tuberculosis. Am J Respir Crit Care Med 2008;177:1164–1170.