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Hyperthyroxinemia associated with high thyroxine binding to albumin in euthyroid subjects
Journal of Endocrinological Investigation
|November 1, 1982
Summary
A genetic condition causes abnormal thyroxine (T4) binding to albumin, leading to falsely high T4 levels in euthyroid individuals. This highlights the importance of accurate thyroid function testing to avoid misdiagnosis of hyperthyroidism.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Genetics
Background:
- Thyroid hormones, primarily thyroxine (T4), regulate metabolism.
- Thyroid function tests typically measure total and free T4 levels.
- Abnormalities in thyroid hormone transport proteins can affect test results.
Observation:
- A euthyroid boy presented with hyperthyroxinemia (elevated total T4) and a high free-T4 index.
- Standard assays for free T4 were normal, with normal thyroxine-binding globulin (TBG) and prealbumin levels.
- Electrophoresis revealed abnormal T4 binding within the albumin fraction of the serum.
Findings:
- The abnormal T4 binding to albumin was sensitive to barbital and affected T3 to a lesser extent than T4.
- This excessive albumin binding explains the discrepancy between high total T4 and normal free T4 levels.
- Two additional family members exhibited similar abnormal T4 binding to albumin.
Implications:
- Accurate diagnosis of thyroid status requires considering abnormal protein binding.
- Misinterpretation of thyroid function tests can lead to misdiagnosis of hyperthyroidism.
- Genetic analysis of thyroid hormone transport may be necessary in select cases.