Serum Thyrotropin Levels of Natives in Sarawak, Borneo Island

A survey of endemic goiter was carried out on natives of Borneo Island, where dietary iodine was deficient. The prevalence of goiter and size of goiter were positively correlated to the age of the subjects. The increase in cumulative prevalence (vide infra) was highest between age 10 and 30, with annual increment approximately 0.5%. Serum TSH was not elevated in all subjects without goiter (less than 5 μU/ml). Mild elevation of TSH up to 20 μU/ml was found in 18% of goitrous subjects, while PBI, T3 resin sponge uptake and free T4 index were not different between goitrous and non-goitrous subjects. When a comparison was made among goitrous subjects, TSH was not significantly elevated in the younger age group in which goiter development was considered active. TSH levels do not correlate with degree of goiter. High 24-hr thyroidal 131I uptake, over 50%, was observed in 71% (15/21 cases) in the face of normal TSH levels. Hence, our findings suggest that TSH seems to be responding to iodine deficiency, rather than causally related to goitrogenesis. Under the circumstance of iodine deficiency, roles of other factors, i.e. autoregulation of the thyroid gland and increased sensitivity to TSH, were discussed.