RT Journal Article SR Electronic T1 Quantitative scoring of an interferon-γ assay for differentiating active from latent tuberculosis JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP 722 OP 728 DO 10.1183/09031936.00028507 VO 30 IS 4 A1 J-P. Janssens A1 P. Roux-Lombard A1 T. Perneger A1 M. Metzger A1 R. Vivien A1 T. Rochat YR 2007 UL http://erj.ersjournals.com/content/30/4/722.abstract AB The aim of this study was to assess the contribution of an interferon-γ release assay (T-SPOT.TB) to the differentiation of active tuberculosis (TB) from latent TB infection by quantifying spot-forming units (sfu). The investigation was a prospective study of contacts exposed to a case of contagious TB and cases of HIV-negative culture-proven TB referred over a 16-month period. Tuberculin skin tests (TSTs) and T-SPOT.TB were performed in 310 contacts 8–12 weeks after exposure. In subjects with culture-proven TB, T-SPOT.TB was performed within 2 weeks of initiation of treatment. The analysis included all contacts with a positive T-SPOT.TB result and all subjects with TB. TB contacts (n = 127) and cases (n = 58) were included. Mean±sd T-SPOT.TB results were 107±56 (range 1–207) sfu for TB, 54±60 (7–239) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of >5 mm, and 19±27 (7–143) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of ≤5 mm. By receiver operating characteristic curve analysis, a threshold value of 49.5 sfu showed a sensitivity of 83% and specificity of 74% for distinguishing latent TB infection from TB. Although T-SPOT.TB results were significantly related to disease activity, the test cannot be recommended for the diagnosis of tuberculosis.