Swiss newborn screening for severe T and B cell deficiency with a combined TREC/KREC assay – management recommendations

The recent introduction of newborn screening for severe primary T and B cell deficiencies in Switzerland allows rapid identification of patients with severe combined immunodeficiency (SCID). Outcomes for SCID are greatly improved by early diagnosis and treatment with allogeneic haematopoietic stem cell transplantation or, in selected cases, gene therapy. National centralised newborn screening is performed in Switzerland since January 2019 using a combined T cell receptor excision circles (TREC) / κ-deleting recombination excision circles (KREC) assay, also revealing infants with non-SCID severe T and B cell disorders, who are often diagnosed with a substantial delay. Here, we outline the screening procedure currently performed in Switzerland and give recommendations for diagnostic evaluations and precautionary measures against infection in children with abnormal screening test results.