Abstract
Screening for hypo- or hyperthyroidism in adults is generally done by measuring the serum thyrotropin (thyroid-stimulating hormone, TSH) concentration. This is an efficient approach in case of suspected acquired thyroid disease. However, in infants and children, congenital hypothalamus-pituitary-thyroid (HPT) axis disorders also need to be considered, including primary and central congenital hypothyroidism, and even rarer thyroid hormone receptor and transporter defects. In primary congenital hypothyroidism, TSH will be elevated, but in the other congenital HPT axis disorders, TSH is usually within the normal range. Free thyroxine (FT4) assessment is essential for the diagnosis in these conditions.Conclusion: Here we discuss a number of rare congenital HPT axis disorders in which TSH is normal, but FT4 is low, and provide a clinical algorithm to distinguish between these disorders.What is Known:• A single thyroid-stimulating hormone (TSH) measurement is an appropriate screening method for primary hypothyroidism.• For central hypothyroidism and rare thyroid hormone receptor and transporter defects a free thyroxine (FT4) measurement is essential for the diagnosis because TSH is usually normal.What is New:• Here we present a new problem-oriented clinical algorithm including a diagnostic flow-chart for low FT4 and normal TSH in infants and children.
Highlights
Biochemical evaluation for suspicion of acquired thyroid disease—i.e. hypothyroidism or hyperthyroidism—in adults starts with measurement of serum thyroid-stimulating hormone (TSH)
Here we discuss a number of rare congenital HPT axis disorders in which TSH is normal, but FT4 is low, and provide a clinical algorithm to distinguish between these disorders
For central hypothyroidism and rare thyroid hormone receptor and transporter defects a free thyroxine (FT4) measurement is essential for the diagnosis because TSH is usually normal
Summary
Low free thyroxine and normal thyroid-stimulating hormone in infants and children: possible causes and diagnostic work-up. Received: 20 November 2020 / Revised: 9 January 2021 / Accepted: 2 February 2021 / Published online: 13 February 2021 # The Author(s) 2021
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