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

Objectives: To 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.
Methods: One-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.
Results: Analysis 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.
Conclusions: The 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.