Comprehensive Thyroid Assessment in a Prospective Japanese Cohort: Epidemiology, Determinants, and Ultrasonographic Reference Ranges

ContextA comprehensive evaluation of thyroid disease and health through multimodal assessment is warranted. ObjectiveTo clarify the epidemiology and clinical significance of abnormal findings on thyroid examinations in a medical checkup setting. DesignProspective cohort study conducted between April 1, 2016, and December 31, 2021. SettingJapanese adults undergoing self-paid medical checkups at the Preemptive Medicine and Lifestyle Disease Research Center, Kyoto University Hospital Main Outcome MeasuresAll subjects underwent thyroid function tests, ultrasonography, and 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET); anti-thyroperoxidase antibody (TPOAb) titers were measured in a subset of subjects. ResultsIn the original cohort of 4,407 subjects (2,643 males and 1,764 females), the prevalence of thyroid dysfunction, increased blood flow on ultrasonography, diffuse thyroid FDG uptake, and thyroid nodules was 5.81%, 2.45%, 3.43%, and 39.71%, respectively; all were more frequent in females. Among 2,420 subjects with TPOAb measurements, TPOAb positivity was 7.19% and was significantly associated with thyroid dysfunction only at titers [≥] 128 IU/mL. Multivariate analyses identified age, sex, and thyroid volume as major determinants of thyroid function. Using data from 1,840 subjects without any thyroid abnormalities, we established sex-specific reference ranges for thyroid dimensions and found their correlations with age and body size. ConclusionsThis cohort provides epidemiological and physiological insights into thyroid health by integrating findings from thyroid function tests, ultrasonography, FDG-PET, and TPOAb measurements. Furthermore, the present study highlights the associations across abnormal findings, relationships within thyroid physiology, and the clinical relevance of high-titer TPOAb.