Frequency and significance of indeterminate and borderline Quantiferon Gold TB IGRA results

What is it about?

The Quantiferon blood test is a standard test used to identify individuals who would benefit from treatment to prevent active Tuberculosis (TB). This is used in clinical practice, for instance in people who have been in contact with cases of active TB, or before starting immune suppressing treatment which would increase the risk of TB. However, sometimes the Quantiferon test does not give a clear "positive" or "negative" result, and it is not clear if using a "borderline" result range is helpful. We used a database of just over 3000 Quantiferon results to evaluate the proportion of results which were not clearly positive or negative, and the effect of repeating borderline results. We found that 8% of results either could not be interpreted, or lay in a borderline area around the cut-off between positive and negative. When these borderline results were repeated the result changed around one third of the time. This suggests that using a borderline range for this test may be helpful to avoid over-treating or under-treating patients.

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