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Non-diagnostic pathology results from TTNB, in the absence of an on-site cytopathologist, are of value in assessing the clinical probability of malignancy and can be useful in the management of lung lesions. However, many other factors should be considered in patients with inadequate specimens.

bPrevious reports have shown that the sensitivity of the 6-day lymphocyte stimulation test is much higher than those of commercially available gamma interferon release assays (IGRAs). The aim of this study was to elucidate the effect of prolonged incubation on the results of the QuantiFERON TB Gold in-tube (QFT-GIT) assay. Patients aged >20 years with suspected tuberculosis (TB) were recruited prospectively from 1 May 2009 to 31 December 2010. In addition, healthy volunteers with no history of TB treatment were included as controls. For each participant, three sets of the QFT-GIT assay were performed using 24-, 48-, and 72-h incubation tests, and the results were compared. Thirty-seven patients with suspected pulmonary TB and 33 healthy controls were enrolled in the study. Of the 37 patients with suspected TB, the QFT-GIT assay results were positive for 28 (75.7%) after a 24-h incubation period. After prolonged incubation, the results differed in four (10.8%) of the 37 patients suspected of having TB. Among 27 patients with culture-confirmed TB, the sensitivities of the QFT-GIT assay after the 24-, 48-, and 72-h incubation tests were 85.2%, 81.5%, and 81.5%, respectively. Among the 33 healthy controls, the QFT-GIT assay results were positive in two (6.1%) after a 24-h incubation period. The results changed for two (6.1%) of the 33 healthy controls after prolonged incubation. The specificities of the QFT-GIT assay after 24, 48, and 72 h of incubation were 93.9%, 87.9%, and 90.9%, respectively. Prolonging the incubation time did not increase the sensitivity of the QFT-GIT assay. The manufacturer-recommended incubation time of 16 to 24 h should be respected because prolonged incubation can cause indeterminate or false-positive results. R ecently, gamma interferon (IFN-␥) release assays (IGRAs) have been introduced into clinical practice as an alternative to the traditional tuberculin skin test (TST) (1, 2). Two IGRAs are available commercially, the QuantiFERON TB Gold in-tube (QFT-GIT) assay (Cellestis, Victoria, Australia) and the T-SPOT.TB assay (Oxford Immunotec, Oxford, United Kingdom). A meta-analysis suggested that the QFT-GIT assay may not be as sensitive as the T-SPOT.TB assay (70% for QFT-GIT assay and 90% for T-SPOT.TB assay) (3), but the QFT-GIT assay is more convenient because it does not require mononuclear cell separation.Since the adoption of the QFT-GIT assay in routine clinical practice, various procedural modifications have been investigated to improve its sensitivity. Incubation without delay (4, 5) and incubation at 39°C rather than 37°C (6) have been reported to increase its sensitivity.Given that the sensitivity of the 6-day lymphocyte stimulation test is much higher than that of IGRA (7), we postulated that prolonged incubation would increase the sensitivity of the QFT-GIT assay for diagnosing Mycobacterium tuberculosis infection. In addition, in routine clinical practice in South Korea, sampling for the QFT-GIT assay is performed between Monday and Thursday and not on Friday. Because the ass...

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