Serum thyroglobulin reference intervals in regions with adequate and more than adequate iodine intake

The purpose of this study was to establish normal thyroglobulin (Tg) reference intervals (RIs) in regions with adequate and more than adequate iodine intake according to the National Academy of Clinical Biochemistry (NACB) guidelines and to investigate the relationships between Tg and other factors. A total of 1317 thyroid disease-free adult subjects (578 men, 739 nonpregnant women) from 2 cities (Guangzhou and Nanjing) were enrolled in this retrospective, observational study. Each subject completed a questionnaire and underwent physical and ultrasonic examination. Serum Tg, thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), Tg antibody (TgAb), and urinary iodine concentration (UIC) were measured. Reference groups were established on the basis of TSH levels: 0.5 to 2.0 and 0.27 to 4.2 mIU/L. The Tg RIs for Guangzhou and Nanjing were 1.6 to 30.0 and 1.9 to 25.8 ng/mL, respectively. No significant differences in Tg were found between genders or among different reference groups. Stepwise linear regression analyses showed that TgAb, thyroid volume, goiter, gender, age, and TSH levels were correlated with Tg. In adults from regions with adequate and more than adequate iodine intake, we found that Tg may be a suitable marker of iodine status; gender-specific Tg RI was unnecessary; there was no difference between Tg RIs in regions with adequate and more than adequate iodine intake; and the TSH criterion for selecting the Tg reference population could follow the local TSH reference rather than 0.5 to 2.0 mIU/L.