PHILADELPHIA — A neonatal screening test for severe combined immunodeficiency was added to Wisconsin's newborn screening panel Jan. 1, making it the first state to screen newborns for the disease.
Although the start-up cost for automating the test was high—requiring installation of $500,000 worth of equipment—and running the test will cost Wisconsin about another $400,000 each year, the anticipated saving in medical costs for treating a single infant who develops complications from severe combined immuno- deficiency (SCID) is about $2 million, Dr. William J. Grossman said at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
Screening for SCID also marks the first time that newborn screening has used a polymerase chain reaction-based (PCR-based) test. This step will likely pave the way for the eventual introduction of several more PCR-based tests into newborn screening, Dr. Grossman, a pediatrician at Children's Hospital of Wisconsin in Milwaukee, said in an interview.
Availability of an inexpensive, PCR-based screening test for SCID led to its being highlighted as a priority for newborn screening last year by the SCID Newborn Screening Working Group (J. Allergy Clin. Immunol. 2007;120:760–8). The group cited the clinical importance of intervening before an infant develops a first infection because of SCID, and the efficacy of treatment by stem-cell transplantation. The survival rate of infants with SCID who are not diagnosed or treated until after they are 3.5 months old is about 66%. That rate is about 96% if diagnosis and treatment occur before infants reach 3.5 months.
Pilot newborn screening done in Wisconsin last year identified a TREC (T-cell receptor-rearrangement excision circles) number of less than 75 per dried blood spot as a signal of SCID. The incidence of newborns who fell into this category was 0.02%. Pilot testing showed that this screen was able to pick up all four true positive SCID specimens that were introduced into the screened specimens. Specimens that screen positive are followed by a flow cytometry test to directly quantify T-cell numbers and confirm the SCID diagnosis.