Endocrine Abstracts

Background: World Health Organization (WHO), United Nations International Children’s Emergency Fund (UNICEF), and the International Council for Control of Iodine Deficiency Disorders included neonatal thyroid stimulating hormone (nTSH) as one of the indicators for assessing iodine deficiency at a population level and as a monitoring tool in programs of iodine supplementation. A prevalence of nTSH concentrations in dry blood spots (DBS) above 5 mlU/l below 3% has been proposed as the threshold indicating iodine sufficiency. Since 1994 WHO and UNICEF reached an agreement to recommend Universal Salt Iodization as a key strategy for prevention and elimination of Iodine Deficiency Disorders worldwide. In Lithuania mandatory universal salt iodization program was implemented in 2005. The aim of this study was to evaluate nTSH data to assess the current status of iodine nutrition in Lithuania.

Methods: The study was conducted as a part of nationwide program NATRIJOD aimed to evaluate sodium and iodine status in Lithuania (the country with 2 784 279 inhabitants in 2021). We retrospectively analyzed the results of nTSH tests from the National Newborn Screening Program for congenital hypothyroidism database between 2002 and 2018. According to screening methodology, heel-prick blood samples of newborns were collected on filter paper cards. Results of samples collected >48 h after birth were analyzed. The nTSH concentration was measured in DBS using fluorometric enzyme immunoassay (Labsystems). Anonymized results of nTSH tests from 492143 cards were retrieved, congenital hypothyroidism cases and inadequately sampled DBS were excluded, frequency of results at the cut-off of nTSH above 5 mIU/l was calculated.

Results: The prevalence of nTSH above 5 mU/l varied between 1.21 % (in 2013) and 5.43 % (in 2004). Since 2011 overall prevalence of nTSH above 5 mU/l was less than 3% and only one region has had frequency above 3% for several years. In 2018 increase in the prevalence of nTSH above 5 mU/l was noted in three regions of the country, indicating possible mild iodine deficiency in these regions.

Conclusions: Despite that children, pregnant women and adult in Lithuania are mildly iodine deficient, based on median urinary iodine concentrations data, the prevalence of nTSH above 5 mU/l was low, suggesting a need to re-evaluate universal cut-off of nTSH and investigate other potential factors impacting nTSH results in order to detect early mild iodine deficiency in population and achieve sustainable elimination of iodine deficiency.