Congenital hypothyroidism and iodine status in Turkey: a comparison between the data obtained from an epidemiological study in school-aged children and neonatal screening for congenital hypothyroidism in Turkey

Abstract

Background: Congenital hypothyroidism and endemic iodine deficiency are the most common cause of mental retardation. However in both cases retardation is of nonpreventable nature.

Objective: The aim of the study was to investigate whether epidemiological study in school-aged children or neonatal screening of congenital hypothyroidism (CH) was useful to assess iodine status and monitor the preventive measures of iodine deficiency disorders (IDD).

Subjects: To study the epidemiology, 1046 school children, aged 8 to 12 years from 23 primary schools in rural and urban areas from three cities in Turkey were included. Neonatal screening for congenital hypothyroidism (CH) was carried in.

Methods: Goiter and thyroid volume were assessed by palpation and ultrasound, respectively. Thyroid stimulating hormone (TSH), total thyroxine (T4), and urinary iodine excretion (UIE) were measured. Neonatal screening for CH was adjusted according to the guidelines of Pediatric Endocrinology of the European Society for Pediatric Endocrinology.

Results: There was no significant difference between the median TSH in school-aged children and the cities of Bolu and Duzce (p>0.05). Median TSH of Zonguldak was significantly different from the median TSH of Bolu (p=0.046) and Düzce (p=0.028). There was no significant difference between the median T4 levels of Bolu and Duzce (p>0.05). The median T4 of Zonguldak showed a significant difference from the median T4 value of Bolu (p=0.018), but an insignificant difference from the median T4 of Duzce (p>0.05). The overall goiter prevalence in 1046 children was 52%. In two years, 18606 newborns were screened. With a cut-off point at TSH >20 microm U/ml, the recall rate was 1.6% and the incidence of CH 1/2326. There was 26.7% children with TSH >5 microm U/ml. Both data of the epidemiological study in school-aged children and neonatal screening for CH indicated that the West Black Sea Region is affected by mild to moderate iodine deficiency.

Conclusion: the implementation of neonatal screening for congenital hypothyroidism using TSH measurement has many advantages. It can detect congenital hypothyroidism and transient primary hypothyroidism, and can also be used for monitoring tools of preventive measures of IDD. Countries, such as Turkey, which has not begun national screening for CH yet, should make implementation of neonatal screening for CH using primary TSH measurement a political priority.