Thyroid gland volume of schoolchildren in the North of Iran: Comparison with other studies

BACKGROUND: Few studies have shown the limitation of the World Health Organization (WHO)/ International Council for the Control of Iodine Deficiency (ICCIDD)-adopted thyroid gland volume references as universal normative values for thyroid gland volume. So we decided to measure thyroid gland volume by sonography in schoolchildren in Rasht, Gilan Province, Iran — Rasht is a metropolitan city on the Caspian Sea coast — and compare them to WHO normative values. MATERIALS AND METHODS: In a cross-sectional study, 2,522 schoolchildren, aged 6-13 years, in Rasht, Gilan Province, Iran were selected by multistage random sampling. Data were collected on their age, sex, weight, height, body surface area (BSA), and thyroid gland size by palpation and sonography. The terminal phalange of thumb finger volume was calculated with the same formula used in sonography, for the thyroid gland in 1,085 of these cases. RESULTS: Goiter prevalence was 64% (1613 cases) by palpation, 76.1% (1228 subjects) grade I and 23.9% (385 cases) grade II. The mean thyroid gland volume in girls was more than boys (3.67 ± 1.89 mL vs 3.41 ± 1.58 mL, P < 0.0001). According to the 1997 WHO thyroid gland volume reference, none of the children had goiter based on BSA and age even in those with grade II goiters (23.9%). In contrast, the median thyroid gland volume in our cases was larger than the 2004 WHO reference. The best single predictor of thyroid gland volume was age (R(2) = 0.391, P < 0.0001) followed by BSA (R(2) = 0.151, P < 0.0001). There was also a significant difference between thyroid gland and finger volume in all grades of goiter and grade II goiters (3 ± 1.4 mL vs 9.59 ± 2.4 mL; P < 0.0001. 4.3 ± 1.4 mL vs 9.3 ± 2.5 mL; P < 0.0001). CONCLUSION: The WHO standards for thyroid gland volume by sonography may underestimate or overestimate the goiter prevalence in many areas and populations. Finger volume was much larger than thyroid gland volume in even visible goiters.