Evaluation of the Immune Response to Interferon Gamma Release Assay and Tuberculin Skin Test Among BCG Vaccinated Children in East of Egypt

Bacille Calmette-Guérin vaccine (BCG) vaccination is used routinely in most of countries, especially developing one. The efficacy of the BCG vaccination generally decreases with time. The tuberculin skin test (TST) is a most popular diagnostic test for suspicion of tuberculosis (TB) in children till now, but it has many false positives. The interferon-gamma release assay (IGRA) is more specific than TST for detection of childhood TB, as it is more specific to Mycobacterium tuberculosis.Evaluate the interferon gamma response and TST reaction in BCG vaccinated children in east of Egypt.150 children were included in the study aged 1 month to 12 years; the collected data from the children included, full history taking, clinical examination, examination for the presence or absence of BCG scar under direct light. All the children had performed TST, IGRA.TST was done for all studied group reveal 51.3% with size of reaction <5 mm, 39.3% with size of reaction = 5 to 9 mm while 9.3% with size of reaction ≥10 mm. Mean size of reaction was 4.07 mm. Interferon gamma release assay was done for all studied group reveal 5 children (3.3%) with positive test. There was significant difference between the size of TST reaction and age (P < 0.01) with old children were more frequent to show positive reaction. Also, children with age range 1 month to 1 year were frequently have negative IGRA test, while children with age range 4 years to 12 years were frequently have positive test (P < 0.01). There was moderate agreement between IGRA and TST results (Kappa [κ] = 0.475). With high agreement between IGRA and TST results in children with absent BCG scar (κ = 1000).Therefore, Interferon gamma release assays have higher specificity and lower cross-reactions with BCG vaccination and nontuberculous Mycobacteraie than TST.