Primary immunodeficiency update and newborn screening.

Most newborns with severe combined immunodeficiency (SCID) appear normal. Hematopoietic stem cell transplant within the first three months of life increases survival and decreases medical costs. Newborn screening measuring T cell receptor excision circles (TREC), a by product of T cell maturation, offers the opportunity for early diagnosis before infections and failure to thrive occur. The Secretary of Health and Human Services recently recommended addition of TREC to newborn screening, enabling prompt diagnosis and effective management of SCID.