Severe Combined Immunodeficiency Disorder and Immunization

August is National Immunization Awareness Month. Health care workers play an important role in educating parents about the importance of vaccination for their infants and older children. Unfortunately, patients with certain conditions are unable to receive some or all vaccinations, leaving them vulnerable to many communicable diseases, such as measles and whooping cough. Patients who are unable to receive vaccines for medical reasons rely on the rest of us to keep our vaccinations updated to protect us against diseases that we can pass on to the unvaccinated. This is called community or herd immunity.

Severe Combined Immunodeficiency Disorder (SCID) is a group of rare disorders caused by mutations in different genes involved in the development and function of infection-fighting immune cells. Infants with a SCID diagnosis can’t receive certain vaccines. They appear healthy at birth but are highly susceptible to severe infections. The condition is fatal, usually within the first year or two of life, unless infants receive immune-restoring treatments, such as transplants of blood-forming stem cells, gene therapy, or enzyme therapy. More than 80 percent of SCID infants do not have a family history of the condition. However, development of a newborn screening test has made it possible to detect SCID before symptoms appear, helping ensure that affected infants receive life-saving treatments.

CLSI’s NBS06, Newborn Blood Spot Screening for Severe Combined Immunodeficiency by Measurement of T-cell Receptor Excision Circles, 1st Edition addresses the detection of SCID by population-based newborn screening (NBS) using dried blood spot (DBS) specimens to measure T-cell receptor excision circles (TREC). Responding to recent US recommendations, the document is intended to facilitate the incorporation of SCID NBS into the routine operation of NBS programs worldwide. Based on extensive input from NBS laboratories, it describes the laboratory tests currently used to measure TREC in DBS by real-time quantitative PCR. The document also describes biological and clinical features of SCID and of other conditions potentially identified by SCID NBS. It provides an overview of laboratory operations including physical layout, instrumentation, TREC assay protocols, automated methodologies, and alternative platforms. The document includes a summary of diagnostic tests used for follow-up of abnormal TREC results as well as other short-term and long-term follow-up activities, including case tracking. It describes variants of SCID that may not be detected by TREC assays in newborn DBS. The guideline delineates the steps for implementing SCID NBS: validating the laboratory test, conducting pilot studies, and transitioning to routine screening. It is directed toward NBS laboratory personnel, public health program personnel, producers of laboratory products related to NBS, and those involved with oversight of NBS testing.