Schoolchildren thyroid volume in North Macedonia: data from a national survey in an iodine-sufficient country

Purpose: North Macedonia is historically iodine deficient, but due to the longstanding and effective preventive measures, it has been considered iodine replete since 2003. The aim of the recent national survey was to re-evaluate iodine status and to measure thyroid volume (TVol) by ultrasound in schoolchildren as a representative of the general population.

Methods: A stratified probability proportionate to size cluster sampling was used to obtain a representative national sample of school children aged 7-10 years between the 28th of March and 4th of October 2016. Thyroid volume (TVol) was measured using ultrasonography in 1188 children. All TVol measurements were done by a single operator and their medians were compared with an international reference standard.

Results: Significant positive correlation was found between Tvol and age, height, weight, body surface area (BSA), body mass index (BMI) in both girls and boys (p < 0.001), but not between TVol and urinary ioidine concentration (UIC). The most important predictors for Tvol in all children were age, height, weight, BMI, and BSA ( all p < 0.001). In multivariate regression, independent predictors for TVol were only BSA (p < 0.001) and age (p = 0.004) after being adjusted for sex, BMI, and UIC (R² = 0.291). The 97th percentile of Tvol in our survey was generally higher than in the reference study and goiter prevalence of 18.3% in boys and 15.6% in girls was found compared to the international standard.

Conclusion: In our survey, Tvol of schoolchildren was larger than in the international reference study, although iodine nutritional status of the country has been considered sufficient for many years. In countries and regions with long and effective, well-documented iodine prophylaxis, the optimal way to have realistic normative TVol would be to create their TVol reference limits. Therefore, the provided data for TVol measured in our survey could be proposed as the national reference TVol for schoolchildren aged 7-10 years.