Agreement between Mycobacterium tuberculosis antigen-based skin test and interferon-gamma release assay in elderly individuals aged ≥65 years in China

Objectives To determine the agreement of Mycobacterium tuberculosis (MTB) antigen-based skin test (TBST) with interferon-gamma release assay (IGRA) in the elderly individuals aged ≥65 years beyond instruction for use in China. Methods Based on the baseline survey of a randomized controlled trial with the objective of exploring suitable regimens for tuberculosis(TB) preventive treatment, MTB infection was tested using TBST and IGRA in parallel in rural residents aged 50-70 years using a cross-sectional study design. Results A total of 21 219 participants with both TBST and IGRA results were included in this analysis. The concordance between TBST and IGRA was 89.4% (95% CI, 89.0-89.8%) with a kappa coefficient of 0.61 (95% CI, 0.60-0.62). In those aged ≥65 years, the concordance was 86.5% (95% CI, 85.6-87.4%) with a kappa coefficient of 0.55 (95% CI, 0.52-0.58). 21.2% (35/165) of the participants with indeterminate IGRA results were TBST positive, and nine of them were aged ≥65 years. Discussion The consistent agreement between TBST and IGRA in individuals aged ≥65 years suggests that TBST has the potential to be used in the elderly with age beyond instruction for use in China. The respective diagnostic performance of each test will be analysed when the longitudinal data on incident TB is obtained in the future.