Establishing Newborn Screening for SCID: The BC and Yukon Experience

Background Severe combined immunodeficiency (SCID) is a life-threatening condition that requires urgent medical attention. Newborn screening (NBS) using the T cell receptor excision circle (TREC) assay facilitates early diagnosis of SCID, which is crucial for improving outcomes. Objectives Describe the diagnoses and outcomes of the first 2.5 years of NBS for SCID in British Columbia and the Yukon, Canada. Methods An interdisciplinary working group of health professionals met at regular intervals prior to and after implementing NBS for SCID. We developed an algorithm for the evaluation and initial management of infants with an abnormal NBS for SCID based on a literature review and local expert consensus. The diagnoses and outcomes of infants with a positive NBS were monitored prospectively. TRECs were measured from dried blood spots of newborns, with the threshold for an abnormal NBS determined using multiples of the median to achieve a positivity rate of 0.1%. Absolute T cell counts less than 1,500 cells/mcL or naïve CD4 or CD8 T cell percentages less than 50% were considered abnormal and prompted immunology consultation. Results and Discussion A total of 110,156 infants were screened between October 2022 and April 2025. There were 2 infants diagnosed with SCID, resulting in a population-based incidence of 1 in 55,078. Both underwent stem cell transplantation within 4 months of life and had no infections at the time of transplant. There was one case of congenital athymia secondary to 22q11 microdeletion syndrome identified by NBS for SCID, who underwent a successful thymic transplantation at 5 months of age. There were no cases of SCID diagnosed outside of the NBS program within this time frame. Conclusion Our experience supports the value of NBS using the TREC assay in facilitating early diagnosis and treatment of infants with SCID.