IFNG and tuberculosis: In Viet Nam, Tuberculin Skin Tests (TST) using Purified Protein Derivative (PPD) Tuberculin Mammalian Bulbio (PPD-Bulbio; BB-NCIPD Ltd., Sofia, Bulgaria) is the preferred diagnostic tool for TBI of the National TB Control Program (NTP) over Interferon-Gamma Release Assays (IGRA)10.