The application of serum iodine in assessing individual iodine status

Summary Context The prevalence of thyroid disease in China is on the rise, and this could be partly associated with excessive iodine intake in some individuals; therefore, increased attention is being paid to individual iodine status. However, current indices are not appropriate for evaluating individual iodine status. Objective To evaluate the association between serum iodine and urinary iodine ( UI ), as well as thyroid diseases, and provide an excellent base for future individual iodine status assessment. Design, subjects and measurements A total of 902 adults were enrolled in this study including 325, 286 and 291 subjects from regions in China where iodine is adequate, sufficient and in excess, respectively. Serum iodine, UI and thyroid function were assessed, and ultrasonography performed in all subjects. Results The median serum iodine values of adults with subclinical hypothyroidism, high serum autoantibody and thyroid nodules were significantly higher than those of euthyroid adults ( P <0.05). A serum iodine level higher than 100 μg/L was considered as a risk factor for thyroid diseases. Serum iodine had strong nonlinear correlations with UI and thyroid function. When thyroid function was taken as a gold standard, the area under the receiver operating characteristic ( ROC ) curve for serum iodine was 0.752 and UI was 0.507 for subjects with lower serum iodine and UI levels. The area for serum iodine was 0.773 and UI was 0.638 for subjects with higher serum iodine and UI levels. The areas under these curves were significantly different ( P <0.001). Conclusion In adults, serum iodine had a strong nonlinear correlation with UI and a high level of serum iodine was a risk factor for thyroid diseases.