Setting: University medical school in Japan.
Objective: To clarify the influence of prior intradermal purified protein derivative (PPD) injection on QuantiFERON-TB Gold (QFT-G).
Design: Ninety-seven sixth-year university medical students aged 20-29 years concurrently underwent QFT-G and tuberculin skin test (TST). The first negative QFT-G and the first TST <15 mm were followed by a second QFT-G one month later.
Results: Five of the 97 (5%) subjects tested positive for the first QFT-G. Thirty-three underwent a second QFT-G, five of whom (15%) turned positive, demonstrating the booster phenomenon of QFT-G.
Conclusions: Prior intradermal PPD injection may boost QFT-G. Further studies of the diagnostic significance and immunological mechanisms of this phenomenon are needed. For clinical application, especially during contact screening, QFT-G should be evaluated while keeping in mind the possible influence of prior PPD intradermal injection.