A multicentre verification study of the QuantiFERON^®-TB Gold Plus assay

Area of Science:

• Immunology
• Infectious Diseases
• Diagnostic Testing

Background:

• Latent tuberculosis infection (LTBI) diagnosis relies on sensitive and specific tests.
• The QuantiFERON^®-TB Gold In Tube (QFT-GIT) is a widely used interferon-gamma release assay (IGRA).
• The newer QuantiFERON^®-TB Gold Plus (QFT-Plus) assay includes an additional antigen tube designed to elicit a CD8+ T-cell response.

Purpose of the Study:

• To compare the performance of the QFT-Plus assay against the QFT-GIT assay.
• To evaluate the utility of the additional antigen tube in the QFT-Plus assay for detecting recent LTBI.
• To assess the CD8+ T-cell response elicited by the QFT-Plus assay.

Main Methods:

• A verification study involving 1031 subjects who underwent both QFT-Plus and QFT-GIT testing.
• Assessment of overall agreement between the two assays.
• Analysis of performance across different test indications and immune states, defining a >0.6 IU/mL interferon-gamma release difference between QFT-Plus antigen tubes as indicative of CD8+ T-cell response.

Main Results:

• High overall agreement (95%) was observed between the QFT-Plus and QFT-GIT assays.
• Subjects with recent tuberculosis exposure showed a significantly greater interferon-gamma release difference between QFT-Plus antigen tubes (p=0.029).
• The QFT-Plus assay demonstrated comparable results to the QFT-GIT assay.

Conclusions:

• The QFT-Plus assay provides results highly comparable to the QFT-GIT assay.
• A notable difference in interferon-gamma release between QFT-Plus antigen tubes may correlate with recent latent tuberculosis infection.
• However, the QFT-Plus assay, in its current form, cannot definitively exclude recent exposure to tuberculosis.