Improved Immunoassay for the Detection of Severe Combined Immunodeficiency

To the Editor: Testing for severe combined immunodeficiency (SCID) has recently become of interest to the newborn-screening community, because the detection of this condition in early infancy is crucial for effective treatment. Several newborn-screening programs have implemented screening for this condition. The current screening method for SCID is by the T-cell receptor excision circles assay (1), which detects the presence or absence of an excised segment of DNA; however, molecular techniques are not routinely adopted in many newborn-screening laboratories, where an immunoassay would be preferred. As recently reported (2), we developed an immunoassay that quantifies CD3, a component of the T-cell receptor complex (3), to provide an alternative or complementary method to T-cell receptor excision circles testing. Low or absent T cells in the peripheral blood is a common characteristic of T-cell immunodeficiencies and of all but one form of SCID. We have previously described an immunoassay using the Luminex microsphere technology that displays excellent potential for the detection of CD3 from dry blood spot samples (2). We report the validation of an improved …