Introducción: neonatal screening programmes are designed for the pre-symptomatic identification and early treatment of treatable congenital diseases, in order to reduce the morbidity and mortality and possible associated disabilities. These programmes have to guarantee equal, universal access for all newborns from the target population, providing correct information to parents to help in the decision-making process. However, neonatal screening should not be commenced if the benefits of their early detection are not clearly defined, and if there are no guarantees for the correct diagnosis, monitoring, and treatment for all children in which the disease is detect by the healthcare system.

Objectives: to evaluate the clinical effectiveness of neonatal screening for severe combined immunodeficiency (SCID) by quantifying T-cell receptor excision circles (TRECs) by PCR (qPCR).

Methods: a systematic review of the literature from the main biomedical databases, including Medline, Embase, Cochrane Library, HTA, DARE, and INAHTA. Two search criteria were used, one focusing on epidemiology, natural history, morbidity, mortality, diagnosis, and treatment without any time limit, and another focusing on screening for the disease. In order to obtain all of the relevant information, the process was completed with a manual review of the bibliography of the included articles, as well as a general internet search of official websites for screening programmes, organisations, and/or scientific associations.  After reading the titles and abstracts of the articles that resulted from the search, a series of studies were selected based on previously established inclusion and exclusions criteria.

Results, discussion and conclusions: See pdf below​