A multicentre verification study of the QuantiFERON (R)-TB Gold Plus assay

Objectives: The aim of this verification study was to compare the QuantiFERON (R)-TB Gold Plus (QFT-Plus) to the QuantiFERON (R)-TB Gold In Tube (QFT-GIT). The new QFT-Plus test contains an extra antigen tube which, according to the manufacturer additionally elicits a CD8(+) T-cell response above the CD4(+) T-cell response. We assessed the value of this tube in detecting recent latent tuberculosis infections. Methods: Between May 2015 and December 2016, 1031 subjects underwent QFT-Plus and QFT-GIT test. Overall agreement between both tests and performance for different test indications and/or immune states was assessed. A difference of > 0.6 IU/mL interferon-gamma release between the two antigen tubes of the QFT-Plus assay was considered a true difference and used as estimation for CD8(+) T-cell response. Results: Analysis of the QuantiFERON tests resulted in an overall agreement between assays of 95%. Subjects considered to be recently exposed to tuberculosis had significantly more often a true difference in interferon-gamma release compared to all other subjects (p = 0.029). Conclusion: Results of QFT-Plus are highly comparable to QFT-GIT. Although there is an indication that a true difference in interferon-gamma release between the antigen tubes is associated with recent latent tuberculosis infection, the QFT-Plus could not be used to exclude recent exposure.