Endocrine Abstracts

Northern Ireland was one of the first participating sites for the UK screening programme for congenital hypothyroidism (CHT) started 40 years ago. This study aimed to explore any changing patterns in incidence over time. Enrolment in the programme has remained high throughout the 40 years (> 98%). The cut-off value for neonatal thyroid stimulating hormone (nTSH) on day 5-8 of life reduced in ~1995 from 10 mU/l to 8 mU/l to improve sensitivity and specificity. There was a steady increase in incidence of CHT over time with an incidence of 26 cases/100,000 livebirths in 1981 vs 71/100,000 in 2019 (P < 0.00001). Results are similar to recent Republic of Ireland data (65/100,000). In ten year blocks the average incidence rose from 28 to 42, 65 and 73/100,000 live births (1980s, 1990s, 2000s and 2010s respectively). Similar increases have been reported in North America, Australia, Italy and Greece. Possible explanations include changes in cohort gestational age or ethnicity, more survivable associated conditions, iodine nutritional status, unquantified environmental changes (e.g., perchlorate exposure), assay cut off change or assay drift. The median gestational age of affected babies did not change significantly e.g. 40 weeks (IQR 39-41) in 1980s vs 39 weeks (IQR 38-40) in 2010s. Ethnicity is not captured in screening data, but census data shows no significant change (95% British/Irish). The most common associated chromosomal abnormality was Trisomy 21 (4.4% overall) with little change over last 30 years. When the data was reanalysed excluding cases with TSH 8-10 mU/l there was still a significant increase in incidence (P < 0.00001). Assay drift is possible but unlikely as our laboratory is UKAS accredited and quality assured. Our data confirms a similar increase in CHT found in other Western countries against a background of a relatively stable population.