Interpretation of normative thyroid volumes in children and adolescents: is there a need for a multivariate model?

The use of thyroid ultrasonography for determination of thyroid volume requires reliable reference criteria. The current World Health Organization/International Council for the Control of Iodine Deficiency Disorders (WHO/ICCIDD) reference has been questioned since iodine-sufficient children have been found throughout the world with distinctly smaller thyroid volumes. A difference in part explained by a systematic bias when generating the WHO/ICCIDD reference data. The objective with this study was to evaluate normative thyroid volumes in our region and, if possible, develop a multivariate model for their interpretation. Thyroid ultrasonography was performed and anthropometrical measurements were taken in 561 children and adolescents. The best predictor for thyroid volume in both girls and boys was body surface area (BSA), followed by age, weight, and height. References for normative thyroid volumes were calculated for each of the predictors. When these references were compared with other references throughout the world, the age-specific references were in good accord, but distinct differences were found between our BSA-specific references and other references based on a majority of children younger than ours. Using multivariate analyses, BSA and age were found to significantly influence thyroid volume, independently of each other. Multiple regression models by gender using BSA and age as predictors for thyroid volume were constructed. Using these models the difference between the BSA-specific references could be markedly reduced. To interpret thyroid volume accurately we propose the use of a multivariate model using age and BSA as predictors of thyroid volume.