Thyroid dysfunction stands as the most prevalent endocrine disorder in individuals with Down syndrome, particularly showcasing both clinical and subclinical hypothyroidism. TSH and FT4 blood values serve as common diagnostic and treatment adjustment markers. In Down syndrome (DS), hormone values may deviate from those observed in the general population, which may lead to overdiagnosis and consequent iatrogenesis of subclinical hypothyroidism. The objective of this study was to analyze the appropriateness of the replacement therapeutic approach by identifying the TSH and FT4 values that can be considered normal in these patients.
Methods: A cross-sectional study was conducted in 503 subjects with DS of both sexes and without age limit drawn from the Health Program for individuals with DS in Valencia (Spain) from February 1993 to November 2021. The exclusion criteria included hyperthyroidism, nodules, tumors, or individuals under treatment with drugs influencing iodine metabolism. The normality of data distribution was assessed using the Shapiro-Wilk test. Outliers were detected using the Reed's criterion. Hormone values were estimated using quantile regression models for the 2.5th and 97.5th percentiles.
Results: The normal values identified were 0.88-11.25 mIU/L for TSH and 0.71-1.63 ng/dL for FT4. The Wald test indicated no significant differences in the reference intervals based on age or sex.
Conclusion: The establishment of these values, which, in people with DS, can be considered unique, is of great importance, allowing a watchful waiting attitude to be maintained before starting replacement therapy that is unnecessarily or adjusting medication in diagnosed cases.
Keywords: Down syndrome; free thyroxine; thyroid hormones; thyroid-stimulating hormone.