Adult thyroid volume determinants and reference values: a Chinese cross-sectional study.

OBJECTIVE: To identify determinants of thyroid volume in adults residing in iodine-sufficient areas and to establish reference value. METHODS: This cross-sectional study included adults from iodine-sufficient regions in Shanxi, Guizhou, and Sichuan. Data collected included thyroid volume, demographic characteristics (age, gender), anthropometric measurements (height, weight, body mass index (BMI), body surface area (BSA)), thyroid nodule status and lifestyle (smoking and drinking). Correlation analysis and multivariable ridge regression were used to identify key predictors, with robustness confirmed by quantile regression. The 97th percentile defined the upper reference limit. RESULTS: Among 9832 adults, median thyroid volume was 6.64 mL, higher in males (7.61 mL) than females (6.07 mL, P < 0.001). BSA exhibited the strongest positive correlation with thyroid volume (r = 0.37, P < 0.001), whereas age showed a weak negative correlation (r = -0.10, P < 0.001). Ridge regression identified BSA (β = 2.215), thyroid nodule status (β = 0.895), and gender (β = -0.806) as the primary determinants. Quantile regression indicated stronger effects of BSA and nodule status at higher volumes. Gender-stratified reference values were determined as 15.47 mL for males and 13.60 mL for females. A gender-specific reference standard integrating BSA, nodule status and height was established. CONCLUSIONS: This study provides validated reference values for thyroid volume in iodine-sufficient adults, aiding public health assessments of iodine status and goiter prevalence. It also supports targeted prevention of iodine deficiency disorders in China.