Neonatal TSH levels in Northern Ireland from 2003 to 2014 as a measure of population iodine status

Congenital hypothyroidism in Northern Ireland: 40 years' experience of national screening programme

OBJECTIVE

The incidence of congenital hypothyroidism (CHT) has progressively increased in several regions around the world but has yet to be evaluated in Northern Ireland (NI). CHT screening programme was introduced in NI in 1980 and has had a relatively unchanged protocol since its inception. The purpose of the study was to evaluate the incidence of CHT in NI from 1981 to 2020 and to explore possible contributing factors to any changes seen over the 40-year period.

DESIGN

This was a retrospective database review of children diagnosed with CHT in NI between 1981 and 2020. Data was collected from the patients' medical (paper and electronic) records, including epidemiological, clinical, laboratory, and radiological features as well as outcomes at 3 years.

RESULTS

Of 800,404 new-borns who were screened for CHT in NI between January 1981 and March 2020, 471 were diagnosed with CHT. There was a steady and significant increase in incidence of CHT over time with an incidence of 26 cases per 100,000 livebirths in 1981 versus 71 cases per 100,000 in 2019 (p < .001). Of these 471, 77 new-borns (16%) were born preterm. The incidence of CHT was observed twice as much in female compared to male new-borns. Diagnostic imaging including radioisotope uptake and thyroid ultrasound scans were performed in 143 cases (30%). Of these, 101 (70%) cases had thyroid dysgenesis and 42 (30%) cases had thyroid dyshormonogenesis. There were 293 (62%) of 471 patients had confirmed permanent CHT, and 90 patients (19%) had transient CHT. Over that period at least 95% of the population were recorded as having United Kingdom/Ireland as country of birth.

CONCLUSION

Our findings demonstrate a nearly tripling of the CHT incidence observed over the last 40 years. This is against a background of a relatively stable population demographics. Future research should focus on the underlying cause(s) of this condition which may include changing environmental exposures in utero.

[Neonatal thyrotropin - indicatior of monitoring of iodine deficiency severity. What's level is considered a «cutoff point»?]

BACKGROUND

The issues of monitoring the effectiveness of iodine deficiency prevention programs are an important component in the process of iodine elimination. Neonatal thyrotropin (TSH) has been used as a criterion for the severity of iodine deficiency since 1994, however, the question of the "cut-off point" of the neonatal TSH level has been widely discussed in the recent literature.

AIM

Evaluate the criterion for neonatal hyperthyroidism above 5 mIU/l from the perspective of monitoring iodine deficiency and establish a «cut-off point» on the model of healthy pregnant women with adequate iodine status.

MATERIALS AND METHODS

A prospective study was conducted in a population of pregnant women in the city of Tyumen, with the formation of observation groups according to the level of iodine excretion in the urine - the main group (with adequate iodine status throughout the entire gestation period) and the comparison group (women with iodine levels less than 150 μg/l). The results of neonatal screening for congenital hypothyroidism in children of women participating in the study were evaluated. The frequency of neonatal TSH above 5mIU/l was assessed in the observation groups. ROC-analysis was performed and a «cut-off point» of the level of neonatal TSH was established as an indicator of iodine deficiency.

RESULTS

The median urinary iodine concentration in the population of pregnant women in Tyumen was 159.05 μg/l, the incidence of goiter was 0.38%, the incidence of neonatal hyperthyroidism above 5 mIU/l was 2.88%, which characterizes adequate iodine intake in the pregnant population women. The frequency of neonatal TSH above 5 mIU/l in newborns from women from the main group was 1.47%, and in the comparison group - 9.3% (p = 0.076). ROC analysis revealed a threshold value of neonatal TSH of 2.77 mIU/l at the cut-off point, which corresponded to the highest value of the Youden index. Urinary iodine concentrations greater than 150 μg/l were predicted for nTSH values below this value.

CONCLUSION

Analysis of databases of neonatal screening for congenital hypothyroidism makes it possible to effectively, quickly and at minimal cost annually assess the iodine status in the population. The established «cut-off point» of neonatal TSH in the model of healthy pregnant women with adequate iodine intake in our work is 2.77 mIU/l, the absence of statistically significant differences in the incidence of neonatal hyperthyroidism above 5 mIU/l from women with different iodine status during pregnancy indicate the need to revise the existing threshold of 5 mIU/l and may be an incentive to conduct large-scale studies in regions with different iodine supply.

The Role of Iodine for Thyroid Function in Lactating Women and Infants

Iodine is a micronutrient needed for the production of thyroid hormones, which regulate metabolism, growth, and development. Iodine deficiency or excess may alter the thyroid hormone synthesis. The potential effects on infant development depend on the degree, timing, and duration of exposure. The iodine requirement is particularly high during infancy because of elevated thyroid hormone turnover. Breastfed infants rely on iodine provided by human milk, but the iodine concentration in breast milk is determined by the maternal iodine intake. Diets in many countries cannot provide sufficient iodine, and deficiency is prevented by iodine fortification of salt. However, the coverage of iodized salt varies between countries. Epidemiological data suggest large differences in the iodine intake in lactating women, infants, and toddlers worldwide, ranging from deficient to excessive intake. In this review, we provide an overview of the current knowledge and recent advances in the understanding of iodine nutrition and its association with thyroid function in lactating women, infants, and toddlers. We discuss risk factors for iodine malnutrition and the impact of targeted intervention strategies on these vulnerable population groups. We highlight the importance of appropriate definitions of optimal iodine nutrition and the need for more data assessing the risk of mild iodine deficiency for thyroid disorders during the first 2 years in life.

Neonatal heel prick screening TSH concentration in the Netherlands as indicator of iodine status

Background

Neonatal Thyroid Stimulating Hormone (nTSH) is proposed as indicator of iodine deficiency in a population. Population’s iodine sufficiency is indicated by a proportion of the newborns less than 3% having nTSH above 5 mIU/L. The aim of this study was to explore the Dutch neonatal heel prick screening TSH data to assess iodine status in the Netherlands and identify determinants and potential confounders of this assessment.

Methods

All newborns born in the Netherlands between 2007 and 2015 with a heel prick collection at day 3-7 were included (n = 1,435,600), except preterm neonates and baby’s with a low birth weight. Total T4 was measured for all children, nTSH was measured in the ~ 20% children with lowest total T4.

Results

The proportion with nTSH > 5mIU/L fluctuated between 0.6-1.3% in 2007-2015. nTSH was significantly associated with laboratory performing the nTSH assay and age of heel prick sampling. The overall increasing trend in proportion nTSH >1mIU/L was confounded by the laboratories with different and changed assays.

Conclusions

The low proportion neonates with high nTSH suggests a sufficient iodine status in the Netherlands. Whether the increased proportion nTSH>1mIU/L over the years is an early indicator of deterioration of the iodine status remains unclear, due to differences and changes in analytical assays. nTSH might be a valuable and inexpensive way to get crude insight in the (trend in) iodine status, but more research is needed on the validity and potential conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-021-00722-4.

Optimal Assessment and Quantification of Iodine Nutrition in Pregnancy and Lactation: Laboratory and Clinical Methods, Controversies and Future Directions

Iodine intake must be boosted during pregnancy to meet the demands for increased production and placental transfer of thyroid hormone essential for optimal foetal development. Failure to meet this challenge results in irreversible brain damage, manifested in severity from neurological cretinism to minor or subtle deficits of intelligence and behavioural disorders. Attention is now being focused on explaining observational studies of an association between insufficient iodine intake during pregnancy and mild degrees of intellectual impairment in the offspring and confirming a cause and effect relationship with impaired maternal thyroid function. The current qualitative categorisation of iodine deficiency into mild, moderate and severe by the measurement of the median urinary iodine concentration (MUIC) in a population of school-age children, as a proxy measure of dietary iodine intake, is inappropriate for defining the degree or severity of gestational iodine deficiency and needs to be replaced. This review examines progress in analytical techniques for the measurement of urinary iodine concentration and the application of this technology to epidemiological studies of iodine deficiency with a focus on gestational iodine deficiency. We recommend that more precise definitions and measurements of gestational iodine deficiency, beyond a spot UIC, need to be developed. We review the evidence for hypothyroxinaemia as the cause of intrauterine foetal brain damage in gestational iodine deficiency and discuss the many unanswered questions, from which we propose that further clinical studies need to be designed to address the pathogenesis of neurodevelopmental impairments in the foetus and infant. Agreement on the testing instruments and standardization of processes and procedures for Intelligence Quotient (IQ) and psychomotor tests needs to be reached by investigators, so that valid comparisons can be made among studies of gestational iodine deficiency and neurocognitive outcomes. Finally, the timing, safety and the efficacy of prophylactic iodine supplementation for pregnant and lactating women needs to be established and confirmation that excess intake of iodine during pregnancy is to be avoided.