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Updated: May 20, 2026

Micro-Colony Forming Unit Assay for Efficacy Evaluation of Vaccines Against Tuberculosis
Published on: July 28, 2023
Quantitative and qualitative QuantiFERON(®)-TB gold in-tube results among groups with varying risks of exposure to
Terri Simpson1, Joyce Fox, Karen Crouse
1Department of Biobehavioral Nursing and Health Systems, University of Washington School of Nursing, Seattle, Washington 98195-7266, USA. tsimpson@uw.edu
Objective:
We sought to describe qualitative and borderline quantitative QuantiFERON(®)-TB Gold In-Tube (QFT-IT; Cellestis, Valencia, CA) results among persons screened in the context of routine reasons, employment, contact investigation, high-risk foreign-born arrivals in the United States ≤ 5 years, and high-risk United States residents >5 years.
Methods:
We performed a retrospective review of 3288 QFT-IT results from a clinical laboratory in the Pacific Northwest from January 2, 2008 to June 5, 2009. Interferon-γ (IFN-γ) responses were quantified as low, borderline, or high for tuberculosis (TB) antigens (IFN-γ [TB]) and a positive mitogen control (IFN-γ [mitogen]), after subtracting a background control (IFN-γ [nil]). Qualitative results were categorized as negative, positive, or indeterminate.
Results:
Quantitative values categorized as borderline, well above, or well below the cut-point were associated with qualitative results for IFN-γ (TB-nil) (χ(2) = 2913.178, degrees of freedom [df] = 4, P < .001) and IFN-γ (mitogen-nil) values (χ(2) = 2559.758, df = 4, P < .001).
Conclusion:
Quantitative data enhance the interpretation of qualitative QFT-IT results for persons with varying risks of exposure.
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