Open Access

Objective: Upper reference values for thyroid volume are 25 mL for men and 18 mL for women. Thyroid volume alters with age, body weight, body height, and iodine status, which is not considered in the current limits. The aim was to develop reference equations, considering age, body weight, and height to calculate individual reference values for thyroid volume. Design: This cross-sectional study used data from 3 independent cohorts (SHIP-START, SHIP-TREND, and KORA-F4) in Germany. SHIP-START-0, a population-based health survey, was carried out in Northern Germany, from 1997 to 2001. SHIP-TREND-0, a second independent sample of the same study region, was carried out between 2008 and 2012. KORA-F4, a population-based health survey, was conducted between 2006 and 2008 in Southern Germany. Methods: A total of 11 549 individuals (51% women) were included in the data analysis. Eight thousand six-hundred and six individuals (45% women) were used as the thyroid-healthy reference population when developing equations. Sex-stratified quantile regression models for the 95th percentile using age, body weight, and height as explanatory variables were performed. Results: The overall reference value was 38.7 mL for men and 28.6 mL for women. According to the established cut-offs, 34% of the overall population would have had goitre compared with 7% when using our equations. Conclusion: Upper reference values for thyroid volume are too low for an adult, previously iodine-deficient population and do not consider age, body weight, and height. Using individualised equations reduces the prevalence of thyroid enlargement substantially and can lead to a decrease in overdiagnoses and the use of medical resources.