Comparison of Tuberculin Skin Test result and interferon gamma response to human PPD in BCG scar positive and negative children

BackgroundThe aim of this study is to compare Tuberculin Skin Test (TST) result and interferon gamma response to human PPD (purified protein derivative), in scar positive and scar negative BCG-vaccinated children.MethodsBetween August 2007 and May 2008 a total of 236 children aged 1–168 months (mean 21 months) admitted to Mofid Children’s Hospital, Tehran, Iran, were enrolled in a cross-sectional study. Each patient was examined for BCG vaccine scar and tested with TST and human PPD-based Interferon Gamma Release Assay (IGRA).ResultsTwo hundred and twenty one cases out of 236 (44% female, 1–168 months, mean age 21 months) were scar positive of whom 95% TST result was negative. Human PPD-based IGRA was positive in 110 (49.8%), negative in 85 (38.4 %) and indeterminate in 26 (11.8%) of scar positive patients.Fifteen children (40% female, 1–156 months; mean age 42 months) were scar negative. All the scar negative cases were TST negative. Human PPD-based IGRA was positive in 10 (66.7%), negative in 4 (26.7%) and indeterminate in 1 (6.7%) of scar negative patients.ConclusionsImmune responsiveness to human PPD antigens in scar positive and negative children may not correspond with results of the Tuberculin Skin Test.