Diagnostic performance of stimulated plasma interferon-gamma inducible protein 10 (IP-10) for diagnosing latent tuberculosis infection in healthcare workers

In the absence of a definitive gold standard for diagnosing latent tuberculosis infection (LTBI) in healthcare workers (HCWs), alternative specific biomarkers are needed. This longitudinal cohort study with baseline testing evaluated the diagnostic performance of stimulated plasma interferon-γ inducible protein 10 (IP-10) for LTBI detection among HCWs in a high tuberculosis (TB)-burden setting, using interferon-γ release assays (IGRAs) as the reference standard. The study was conducted at Songklanagarind Hospital, Thailand, between 2021 and 2024, and included 64 healthy HCWs. Serum and stimulated plasma samples were collected, and IP-10 and IFN-γ concentrations were measured by ELISA. Nine HCWs (14.0%) were LTBI-positive. Stimulated plasma IP-10, but not serum IP-10, showed significant correlations with IFN-γ levels in TB1 (r = 0.719) and TB2 (r = 0.768; p < 0.0001) tubes. At cut-off values of ≥ 2,980.0 pg/mL for TB1 and ≥ 3,108.0 pg/mL for TB2, sensitivity was 100%, specificity was 96.0% and 94.5%, and overall accuracy was 96.8% and 95.3%, respectively. Based on either IGRA or stimulated plasma IP-10 cut-off levels, five of nine LTBI cases declined treatment; among these, one individual (20.0%) progressed to active pulmonary TB 16 months later. Stimulated plasma IP-10 shows high diagnostic performance for LTBI detection among HCWs and may serve as an alternative for LTBI screening in high-TB-incidence with universal BCG vaccination.