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

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.