Introduction: Early detection of congenital hypothyroidism (CHT), and treatment with oral thyroxine, supports the critical period of early brain development, improves growth and prevents the metabolic effects of adult hypothyroidism. Screening for CHT, involving an assay for thyroid-stimulating hormone (TSH), has been included in the UK newborn blood spot screening programme since 1981. Since the introduction of screening, the number of CHT cases has increased, although the reasons for this are unclear. There has been limited evaluation of the performance of the current UK programme.
Methods: UK-wide active surveillance to estimate the current incidence of CHT in infancy and to evaluate perfomance of the newborn screening programme. Surveillance was conducted through the British Paediatric Surveillance Unit and newborn screening laboratories from 2011 to 2012 to identify children aged <5 years who were investigated after a presumptive-positive screening result or clinical presentation. Children were followed for 3 years to confirm CHT diagnosis and clinical management. Differences in the TSH assay cut-off used by English laboratories provided an opportunity to explore the optimal screening test cut-off.
Results: Six hundred and twenty nine newborns (58.3% girls) were reported after presumptive-positive screen and an additional 21 children (52.4% girls) after clinical presentation. 508 children commenced thyroxine but this was discontinued in 76 (15%) children. 432 (85%) remained on treatment at three years. Incidence of CHT was 5.3 (95%CI 4.8, 5.8) per 10,000 live-births. Screening programme sensitivity, specificity and positive predictive value were 96.76%, 99.97% and 66.88% respectively. Evaluation at different TSH cut-offs suggested that the optimal cut-off was likely to be lower than the recommended standard.
Discussion / Conclusion: Performance of the UK screening programme for CHT is good, however standardisation of screen test cut-offs is advisable and re-evaluation of the recommended cut-off is warranted. Clinical follow-up is essential to avoid unnecessary continuation of therapy, and ascertain longer-term outcomes.