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Updated: Jan 21, 2026

A Tuberculosis Molecular Bacterial Load Assay TB-MBLA
Published on: April 30, 2020
Variation in interferon-γ production between QFT-Plus and QFT-GIT assays in TB contact investigation
Mizue Tsuyuzaki1, Hidetoshi Igari2, Nao Okada1
1Chiba Foundation for Health Promotion and Disease Prevention, 32-14 Shin-Minato Mihama-ku Chiba, Chiba, 261-0002, Japan.
Background:
Individuals with recent contact with active tuberculosis (TB) patients were screened for latent tuberculosis infection (LTBI) considering their greater relative risk for developing active TB. QuantiFERON®-TB Gold Plus (QFT-Plus) assay offers two TB-specific antigen tubes (TB1 and TB2). TB2 is designed to elicit both CD4 and CD8 T-cell responses. This mechanism could lead to increased sensitivity as compared to the QuantiFERON®-TB Gold In-Tube (QFT-GIT) assay. Our objective was to compare the LTBI diagnostic capability of QFT-Plus with that of QFT-GIT.
Methods:
A total of 412 TB contacts (median age 44 years) were prospectively enrolled. We conducted both QFT-Plus and QFT-GIT assays concurrently. We also analyzed production of interferon-γ (IFN-γ) in response to TB-specific antigens.
Results:
The positivity rates in QFT-Plus and QFT-GIT were 7.5% (95% confidence interval (CI), 5.4-10.5) and 5.8% (CI, 3.9-8.5), respectively, showing a significant difference (P < 0.05). The median (inter-quartile range [IQR]) of IFN-γ[QFT-Plus]/IFN-γ[QFT-GIT] was 1.41 (1.00-2.00). QFT-Plus produced 1.4 times IFN-γ.
Conclusions:
QFT-Plus revealed significantly higher positivity rate compared with QFT-GIT, which might be attributed to increased IFN-γ production. The cut-off in both QFT-Plus and QFT-GIT was 0.35 IU/mL. These effects might resulted in the higher positivity rate in QFT-Plus.
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