Within-subject variability of tuberculosis immune responses in health care workers

Background: Although IFN-γ release assays (IGRAs) are increasingly used for periodic tuberculosis (TB) screening of health care workers (HCWs), data regarding the interpretation of IGRA results in serial testing is scare. Objective: To evaluate the within-subject variability of two commercial IGRAs, QuantiFERON®-TB Gold In-Tube (QFT) and T-SPOT®. TB (T-SPOT). Methods: Thirty-four immunocompetent German HCWs (age 42±10 yrs, 79% female) without recent TB exposure or other individual risk factors were repeatedly tested with both IGRAs in weekly intervals over a four week period. Results: According to the manufacturers9 predefined dichotomous cut-offs 10 (29.4%) and 3 (8.8%) of the 34 subjects had divergent overall trends with the QFT and the T-SPOT, respectively (p Conclusions: We observed considerable variability with both IGRAs and a tendency towards regression of IGRA results over a 4-week period, which should be considered when interpreting repeated IGRA results.