Borderline QuantiFERON results and the distinction between specific responses and test variability

Abstract Background QuantiFERON (QFT) results near the cut-off are subject to debate. We aimed to investigate which borderline QFT results were due to Mycobacterium tuberculosis ( Mtb )-specific responses or to test variability. Methods In a contact investigation, tuberculin skin test (TST), QFT and T-SPOT. TB (T-SPOT) were performed in 785 BCG-unvaccinated contacts. Contacts with a low-negative ( Results Borderline QFT results occurred in threefold excess over test variability (p = 0.0027). In contacts with low-negative, borderline or positive QFT results, a positive TST occurred in 24.9%, 62.1% and 91.4% (p  Mtb -infection. During 12 years of follow-up, seven patients were diagnosed with active tuberculosis, two of whom after a low-positive QFT. Conclusions In this study, most borderline and low-positive QFT results were Mtb -specific, showing the biological significance of a borderline QFT. The clinical relevance, however, will be most distinct in patients who are or will be immunocompromised.