Comparison of the sensitivity and specificity of two whole blood interferon-gamma assays for M. tuberculosis infection

SummaryObjectivesTo compare the sensitivity and the specificity of the QuantiFERON®-TB Gold (QFT-G) and QuantiFERON®-TB Gold In Tube (QFT-GIT) diagnostic tests for Mycobacterium tuberculosis infection.MethodsOne-hundred patients with culture and/or PCR confirmed M. tuberculosis infection and 168 volunteers with no risk factors for M. tuberculosis infection were tested to estimate sensitivity and specificity, respectively.ResultsAnalysis of data from the tuberculosis (TB) patients with valid results found the sensitivity of QFT-GIT (92.6%, 87/94) to be significantly higher than that for the QFT-G test (81.4%, 79/97; p = 0.023). The specificity of both QFT-GIT and QFT-G was 98.8% (CI: 95.1%–99.8%) with 2 of the 160 low risk subjects with valid results for both tests being positive. Data analysis confirmed the manufacturer's recommended test cut-off as being optimal, but identified higher sensitivity could be obtained by using a lower cut-off, with only a moderate decrease in specificity.ConclusionsThe QFT-GIT test had enhanced sensitivity for detection of M. tuberculosis infection over the QFT-G test, whilst maintaining equivalent high specificity. The logistic benefits of the QFT-GIT test format, as well as its higher sensitivity, should enable enhanced TB control.