Exploiting KREC: Time for newborn screening and beyond-proceedings from the First International KREC Consortium...

Newborn screening (NBS) for severe combined immunodeficiency using T-cell receptor excision circles has changed the diagnosis and outcomes for infants with profound T-cell lymphopenia. However, patients with severe B-cell lymphopenia are still typically diagnosed only after serious or recurrent infections or irreversible complications. Some countries now measure kappa-deleting recombination excision circles (KREC) together with T-cell receptor excision circles to identify infants with severe B-cell lymphopenia, but adoption remains limited. The First International KREC Consortium Meeting, held in Tampa, Florida, in February 2026, convened clinicians, laboratory scientists, public health experts, patient advocates, and families from North America, Europe, Asia, and South America to review current experience and implementation strategies for broader KREC screening. Sessions covered international screening programs, laboratory methods, assay harmonization, interpretation and reporting, clinical impact of early diagnosis, therapeutic options, and policy pathways for implementation. Patients and families shared personal experiences of delayed diagnosis and perspectives on NBS. The meeting identified key priorities for future implementation, including the justification of this assay on the basis of impact in patient care and feasibility for integration into current NBS approaches on the basis of health-economic evaluation. Once implemented, next steps include harmonization of methods and reporting, strategies to minimize false-positive results and referrals, and follow-up pathways. These proceedings summarize the major discussions and outline priorities for collaborative evidence generation and future implementation.