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Tuesday, 29 March 2016 10:30

Paper 2016_03

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Sensitivity of C-Tb: a novel RD-1-specific skin test for the diagnosis of tuberculosis infection


Soren T. Hoff, Jonathan G. Peter, Grant Theron, Mellissa Pascoe,

Pernille N. Tingskov, Henrik Aggerbeck, Daniel Kolbus, Morten Ruhwald,

Peter Andersen and Keertan Dheda



C-Tb, a novel Mycobacterium tuberculosis and 6-kDa early secretory antigenic target/10-kDa culture filtrate protein (ESAT-6/CFP-10)-specific skin test, has high specificity in bacille Calmette–Guerinvaccinated healthy controls. However, the sensitivity of C-Tb has hitherto not been determined. The objective was to determine the sensitivity of C-Tb in patients with active tuberculosis (TB) in comparison with the tuberculin skin test (TST) and QuantiFERON-TB Gold In-Tube (QFT-GIT). C-Tb and TST were randomly administered in a double-blinded fashion to one or the other forearm in 253 patients with active TB with or without HIV co-infection. QFT-GIT testing was performed prior to skin testing. Using a receiver operating characteristic curve-derived cut-point of 5 mm, C-Tb sensitivity was similar to QFT-GIT (73.9 (95% CI 67.8–79.3) versus 75.1 (95% CI 69.3–80.2)), and similar in HIV-infected and HIV uninfected patients (76.7 (95% CI 69.0–83.3) versus 69.5 (95% CI 59.2–78.5)). However, sensitivity was significantly diminished in HIV-infected patients with CD4 counts <100 cells·mm–3. C-Tb and QFTGIT combined had significantly higher sensitivity than C-Tb alone (p<0.0001). C-Tb was safe with no significant adverse events. The 5 mm cut-point corresponded to that found in the previously published specificity study (TESEC-04). C-Tb has similar sensitivity compared with QFT-GIT for the diagnosis of M. tuberculosis infection. Sensitivity was reduced only in HIV infected patients with severe immunosuppression. Further studies in different settings are required to validate the proposed 5 mm cut-point.


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