Interferon Gamma Release Assay Results and Testing Trends Among Patients Younger Than 2 Years Old at Two US Health Centers

Abstract

Background: Interferon-gamma release assays (IGRAs) are approved for children ≥2 years old to aid in diagnosis of Mycobacterium tuberculosis (TB) infection and disease. Tuberculin skin tests (TSTs) continue to be the recommended method for diagnosis of TB infection in children <2 years, in part due to limited data and concern for high rates of uninterpretable results.

Methods: We performed a retrospective cohort study of IGRA use in patients <2 years old in 2 large Boston healthcare systems. The primary outcome was the proportion of valid versus invalid/indeterminate IGRA results. Secondary outcomes included concordance of IGRAs with paired TSTs and trends in IGRA usage over time.

Results: A total of 321 IGRA results were analyzed; 308 tests (96%) were valid and 13 (4%) were invalid/indeterminate. Thirty-seven IGRAs were obtained in immunocompromised patients; the proportion of invalid/indeterminate results was significantly higher among immunocompromised (27%) compared with immunocompetent (1%) patients ( P < 0.001). Paired IGRAs and TSTs had a concordance rate of 64%, with most discordant results in bacille Calmette-Guérin-vaccinated patients. The proportion of total TB tests that were IGRAs increased over the study period (Pearson correlation coefficient 0.85, P < 0.001).

Conclusions: The high proportion of valid IGRA test results in patients <2 years of age in a low TB prevalence setting in combination with the known logistical and interpretation challenges associated with TSTs support the adoption of IGRAs for this age group in certain clinical scenarios. Interpretation of IGRAs, particularly in immunocompromised patients, should involve consideration of the broader clinical context.