Quantitative and qualitative QuantiFERON(®)-TB gold in-tube results among groups with varying risks of exposure to tuberculosis.

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.