European Society of Mycobacteriology - Instituto Nacional de Saúde ...

QUANTIFERON-TB GOLD ASSAY (QFT) AND TUBERCULINE SKIN TEST (TST)
CLINICAL PERFORMANCE FOR THE DIAGNOSIS OF ACTIVE TUBERCULOSIS
PP-70
Karabela Simona, Papaventsis Dimitrios, Nikolaou Stavroula, Konstantinidou Efthimia, Sainti Asimina, Ioannidis Panayotis,
Kanavaki Sofia
National Reference Center for Mycobacteria, “Sotiria” Hospital, Athens, Greece
Objective
The purpose of this study was to evaluate and compare Quantiferon-TB Gold In-Tube (QFT, Cellestis, Australia) and the
tuberculine skin test (TST) in patients with active TB, with and without previous BCG vaccination.
Methods
Patients with symptoms compatible with active TB were included. The TST was performed according to the Mantoux
method and the QFT assay according to the manufacturer’s instructions. The cut-off value for a positive result was ≥0.35
IU/ml interferon-gamma (IFN-γ). Sensitivity, specificity, positive and negative predictive values were calculated and compared
for QFT and TST tests. Agreement between QFT and TST was assessed by the kappa (κ) coefficient.
Results
A total of 296 patients were enrolled in the study. One hundred eighty-nine had a record regarding BCG vaccination.
Forty-four (23%) of the 189 patients had been vaccinated. In total, the sensitivity and specificity of QFT, excluding those
with indeterminate results, was 79% (52/66; 95% CI: 66-88%) and 66% (153/167; 95% CI: 58-73%), respectively. The sensitivity
and specificity of TST was 72% (46/64; 95% CI: 58-83%) and 67% (156/232; 95% CI: 59-74%), respectively. The overall
concordance between the QFT and TST tests was 70.2%, with a kappa value of 0.46 (95% CI: 0.289-0.524). In the BCGvaccinated
subgroup, agreement between the two assays was 66%, with a kappa value of 0.350 (95% CI: 0.103-0.597). The
difference with the non-vaccinated subgroup (κ=0.463; 95% CI: 0.303-0.623) was considered to be not quite statistically
significant (p>0.05). Initial TST positive screening followed by a QFT positive result was found to have greater sensitivity
and specificity in the non-vaccinated [sensitivity=79% (95% CI: 59-92%); specificity=81% (95% CI: 71-88%)] compared to
the BCC-vaccinated subgroup [sensitivity=67% (95% CI: 30-92%); specificity=75% (95% CI: 57-89%)].
Conclusion
This study confirmed previous reports that QFT assay has higher sensitivity for detecting active TB compared to TST.
An overall moderate agreement between TST and QFT was found. The difference in agreement between non-vaccinated
and BCG-vaccinated subgroups could be attributed to TST influence by vaccination. In patients with active TB and no
BCG-vaccination history, TST screening followed by subsequent QFT testing proved to present the highest sensitivity
and specificity for TB diagnosis. Larger prospective studies are needed to confirm our results.
142 ESM 2009