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Neonatal TSH levels suggest emerging iodine deficiency in Northern Ireland
Researchers have observed an increasing prevalence of neonatal thyroid-stimulating hormone levels greater than 2 mIU/L in Northern Ireland, suggesting an emerging modest iodine deficiency in the region, according to findings published in Clinical Endocrinology.
“Within the U.K. and Ireland, for many years, iodine intakes were thought to be adequate,” Karen Mullan, MD, of the Regional Centre for Endocrinology and Diabetes, Royal Victoria Hospital Belfast, and colleagues wrote in the study background. “More recently, a survey in 2011 reported iodine levels in over 700 teenage girls living across the U.K. Results suggested that this group were mildly iodine deficient, with a median urinary iodine concentration of 80 g/L. Published data from the Republic of Ireland also indicated mild deficiency in the general population in the 1990s, and more recently, in pregnant women.”
Researchers reviewed the neonatal TSH results from a heel-prick screening program conducted across Northern Ireland between 2003 and August 2014.
According to a proposed definition from WHO, population iodine sufficiency is characterized as less than 3% of the population with neonatal TSH results greater than 5 mIU/L. The researchers calculated population iodine sufficiency prevalence rates based on two cutoffs: greater than 2 mIU/L and greater than 5 mIU/L. Seasonal disparities in neonatal TSH results were also assessed.
The researchers found that between 2003 and 2014, 6.2% of infants had a blood TSH level greater than 2 mIU/L and 0.49% had a TSH level greater than 5 mIU/L. The percentage of TSH concentrations greater than 5 mIU/L did not exceed 3% during any year of the study.
The researchers found that, at a cutoff of greater than 5 mIU/L, there was an overall population prevalence of 0.49%, suggesting iodine sufficiency for all years evaluated. Neonatal TSH values greater than 2 mIU/L decreased in prevalence to 4.1% in 2007, and increased to 9.8% in 2014. The researchers also noted a mild seasonal disparity in both neonatal TSH cutoffs; for the cutoff of greater than 5 mIU/L, the fitted peak was in early May, whereas the cutoff of greater than 2 mIU/L peaked in early April, they wrote.
The proportion of neonatal TSH levels greater than 10 mIU/L was 0.13%, and the percentage greater than 20 mIU/L was 0.06%. No indication of seasonality was seen with either of these cutoffs.
“This article is the first publication of its kind from Northern Ireland and one of the largest cohorts in the U.K.,” the researchers wrote. “Results suggest no severe iodine deficiency in this population using over 280,000 [neonatal] TSH samples. Given the controversy with WHO recommendations, we feel the data is useful to the current debate on population monitoring for iodine deficiency.” – by Jennifer Byrne
Disclosures: The authors report no relevant financial disclosures.