The abstract concludes
Different blood tests for the diagnosis of latent tuberculosis infection in children seem to perform differently, because both QuantiFERON-TB tests were more likely than T-SPOT.TB to give indeterminate results in childrenhowever it is worth reading the full text;
QFT-IT and T-SPOT.TB have both been approved for clinical use by the US Food and Drug Administration, although with some minor modifications in the interpretation of T-SPOT.TB results, compared with the European package insert. This reflects the vast amount of published data available.It should be noted that this retrospective study of samples taken between January 2004 and July 2007 predates the approval of T-Spot TB in the US and the performance of the T-Spot TB was not evaluated in accordance to limits as set out in the FDA approval.
Therefore, it is predictable that IGRAs will rapidly become routine in clinical practice. At that point, differences with the standard TST will be particularly relevant. One such difference is the 3-way response of IGRAs (positive, negative, or indeterminate/invalid), compared with the 2-way response of the TST test (positive or negative).
However, the meaning and the impact of indeterminate IGRA results in clinical practice have not been properly evaluated. For now, these results should caution clinicians to be aware of potential false-negative results. In addition, although the difference in the frequency of indeterminate results between the QFTs and T-SPOT.TB in our study was striking, the clinical impact of this difference might be relatively small, because almost all indeterminate QFT results were negative with T-SPOT.TB.
Another interesting finding of our study is the significantly higher concentration of IFN-y produced in QFT-IT compared with QFT-G. Whether this is a consequence of the in-tube format or some other technical factor (such as shaking of tubes), and whether it has an impact on antigen-specific responses, merits additional attention.
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