Endocrine Abstracts

Background: Congenital hypothyroidism (CH) is one of the most common preventable causes of mental retardation and intellectual disability. The overall incidence of CH ranges from 1 in 3,000 to 1 in 4,000 live births, with variation worldwide among different ethnicity [1]. During the period 1993–2000 the incidence of CH in Lithuanian population was estimated as 1 in 4800 live births [2]. The aim of present study was to determine the incidence of CH among new-borns in Lithuania.

Methods: The study was conducted as a part the nationwide NATRIJOD program aimed to evaluate sodium and iodine status in Lithuania. We retrospectively analyzed the results of neonatal thyroid-stimulating hormone (nTSH) tests from the National new-born Screening Program for congenital hypothyroidism database during the period 2002–2019; this reflected about 18% of the total population. According to the screening methodology, heel-prick blood samples of new-borns were collected on filter paper cards. Results of samples collected more than 48 h after the first feeding were analyzed. The nTSH concentration was measured in dry blood spots (DBS) using a fluorometric enzyme immunoassay (Labsystems). Anonymized results of nTSH tests from 517498 cards were retrieved in total. Inadequately sampled 640 DBS were excluded, data of 516858 live-borns were analysed. New-born screening for CH was based on measuring nTSH using a 10 mU/l cut-off and diagnosis of CH was confirmed after repeated evaluation of new-born.

Results: Total of 100 new-borns were diagnosed with CH during study period. Number of CH each year was different lowest in 2004 – 3 cases with CH and highest in 2008 – 17 cases of CH. The highest incidence of CH in Lithuania was observed in 3 counties – Vilnius (29 cases during 19 years), Kaunas (34 cases during 19 years) and Klaipeda (13 cases during 19 years), where 60% of the country’s population live. During the period 2002–2019 the incidence of CH in Lithuanian population was estimated as 1 in 4784 live births.

Conclusions: The overall incidence of CH is low in Lithuania. The study revealed significant geographical variations of CH incidence in Lithuania, depending on population density.

Reference: 1. Deladoëy J, Ruel J, Giguère Y, Van Vliet G. Is the incidence of congenital hypothyroidism really increasing? A 20-year retrospective population-based study in Québec. J Clin Endocrinol Metab. 2011;96(8):2422-9.

2. Jusciene D, Kucinskas V. The etiology, diagnosis and prevalence of congenital hypothyroidism in Lithuanua. Laboratorine Medicina. 2001;3(11):29-34.