Effect of Prolonged Incubation Time on Results of the QuantiFERON TB Gold In-Tube Assay for Diagnosis of Latent Tuberculosis Infection

Abstract

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...

Screening for Latent Tuberculosis Infection in Adults

“…TB , 12 reported on QFT-Gold Plus, and 51 reported on QFT-GIT (eTables 11 and 13 in the Supplement). Nineteen studies were conducted exclusively or partly in the US . Pooled estimates for sensitivity and specificity of TST by induration threshold and of IGRAs by assay are summarized in Table 1 (greater detail is provided in eFigures 1-29 in the Supplement).…”

Reproducibility of Interferon Gamma (IFN-γ) Release Assays. A Systematic Review

“…Other possible sources of variability appeared to have no impact on QuantiFERON results: variation of incubation duration (comparing 20 h and 24 h to a baseline of 16 h [34], and 48 h and 72 h to 24 h [36]), or storage temperature of tubes before testing (37 8 C for 3 months compared with ,25 8 C) (37). Simply repeating optical density measurements of the ELISA test result after a time interval (up to 2 h) did not result in any variability (22,30).…”

Differential activation of innate and adaptive lymphocytes during latent or active infection with Mycobacterium tuberculosis

“…In individuals that were infected with Mtb many years ago, the number of circulating effector memory T cells may be low, and it has been suggested that an incubation period of 24 h could be insufficient to detect IFN‐γ production 16 . However, longer incubation times (24 and 72 h) do not increase the sensitivity or the specificity of QFT, and can cause false‐positive or indeterminate results 21 . For this study, all the QFTs were performed with an incubation period of 20 h.…”

“…16 However, longer incubation times (24 and 72 h) do not increase the sensitivity or the specificity of QFT, and can cause false-positive or indeterminate results. 21 For this study, all the QFTs were performed with an incubation period of 20 h.…”