Newborn screening for severe combined immunodeficiency in the NHS newborn blood spot screening programme: a systematic review.

BACKGROUND: Severe combined immunodeficiency is an inherited condition arising from mutations in at least 19 known genes. Severe combined immunodeficiency can be identified through screening, family history or clinical presentation. Severe combined immunodeficiency is usually asymptomatic at birth and presents, in infancy, as recurrent and frequently severe infections. Without treatment, severe combined immunodeficiency is usually fatal in the first year of life.

OBJECTIVES: To summarise the available evidence relevant to newborn screening for severe combined immunodeficiency in the UK NHS newborn blood spot screening programme. Three research questions, concerning the accuracy of screening tests, the efficacy of early treatment and the acceptability of screening, were developed to address this objective.

METHODS: Eleven bibliographic databases were searched for relevant studies from 2011 to April 2024. Separate inclusion criteria were specified for each research question. Study selection, data extraction and assessment of methodological quality followed standard systematic review methods. A narrative synthesis of results is presented, structured by research question. No meta-analyses were conducted.

RESULTS: Most positive predictive values, calculated from reports of newborn blood spot screening programme experience, were between 3.6% and 26%. Screening algorithms incorporating repeat sampling in preterm babies appeared to reduce false positives due to prematurity. However, the large number of other conditions that can give rise to a positive screening result mean that the positive predictive value for severe combined immunodeficiency remains consistently poor. Two small studies reported that early diagnosis of severe combined immunodeficiency, via newborn blood spot screening or family history and following the introduction of newborn blood spot screening, respectively, was associated with non-statistically significant improvements in post-transplant survival. A third study analysed data on n = 902 United States patients with severe combined immunodeficiency collected over a 28-year period and reported the results of multivariable Cox regression analyses, adjusted for demographic disease-related and transplant-related variables found to be significant on univariate analysis, showing that diagnosis of severe combined immunodeficiency via newborn blood spot screening significantly improved survival compared to diagnosis via clinical presentation. Qualitative data from the publications included in this evidence summary were generally indicative of parental support for newborn blood spot screening for severe combined immunodeficiency, but was mainly derived from parents of healthy newborns.

LIMITATIONS: The systematic review component of this evidence summary was limited by a restriction to full publications in the English language.

CONCLUSIONS: The current published evidence base alone is not adequate to fully support implementation of newborn blood spot screening for severe combined immunodeficiency. With respect to UK National Screening Committee population screening criteria, criterion 4 was partially met and there was insufficient evidence to adequately assess whether criterion 6 was met. The findings of this evidence summary should be considered alongside findings from the recent in-service evaluation of newborn screening for severe combined immunodeficiency conducted in the NHS in England and the results of cost-effectiveness modelling.

FUTURE WORK: Further work is needed to inform policy on how the identification of non-severe combined immunodeficiency T-cell lymphopenia conditions by screening should be treated. Stakeholder dialogue and patient and public involvement activities may be helpful. In particular, the views of parents who have lived experience of a non-severe combined immunodeficiency (incidental) finding from newborn blood spot screening for severe combined immunodeficiency should be sought.

STUDY REGISTRATION: This study is registered as PROSPERO CRD42024544200.

FUNDING: This award was funded by the National Institute for Health and Care Research (NIHR) Evidence Synthesis programme (NIHR award ref: NIHR168307) and is published in full in Health Technology Assessment; Vol. 30, No. 45. See the NIHR Funding and Awards website for further award information.