e324 13th International Congress on Infectious Diseases Abstracts, Poster Presentations Australia) detect interferon-gamma (IFN-␥) production in whole blood samples in response to stimulation with TB antigens. The role of QFT and Tuberculin skin test (TST) in the diagnosis of active TB among adults in high burden countries is not clear. Methods: We prospectively evaluated pulmonary and extrapulmonary TB suspects from a tertiary center in India, in a blinded comparison of new diagnostic tests.

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... aim to recruit 200 patients for the study. The blood samples collected from the patients were processed as per manufacturers instructions. The cut off for positivity used was 0.35 IU/ml. TST was performed using 2TU dose and 10 mm or greater was considered positive. Both were evaluated against a combined gold standard of solid (Lowenstein Jensen) and liquid (BACTEC 460 TB) culture. Results: To date the results of QFT and culture for 51 patients are available. Four indeterminate results were not included. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) of QFT for culture positive TB were 81% (54-95), 67% (47-82), 57% (35-76) and 87% (65-96) respectively. 52 patients had TST and culture results available. The sensitivity, specificity, PPV and NPV of TST for culture positive TB were 68% (45-85), 50% (32-68), 50% (32-68) and 68% (45-85) respectively. Conclusion: QFT has adequate sensitivity but poor specificity to detect active TB in India. QFT shows a trend to better sensitivity than TST. As expected, latent TB infection causes false positives. QFT is a single visit test with good negative predictive value but should not be used alone to rule out active TB.