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Euthyroid hyperthyroxinemia due to familial excess of thyroxine-binding globulin
1Division of Endocrinology, Nalle Clinic, Charlotte, NC 28207.
Southern Medical Journal
|March 1, 1989
Summary
Familial euthyroid hyperthyroxinemia, caused by increased thyroid-binding globulin (TBG) production, can be diagnosed through specific TBG testing. This diagnosis prevents unnecessary thyrotoxicosis treatment for affected families.
Area of Science:
- Endocrinology
- Genetics
- Clinical Diagnostics
Background:
- Thyroid hormone levels are crucial for diagnosing thyroid disorders.
- Benign hyperthyroxinemia can be mistaken for thyrotoxicosis, leading to misdiagnosis and inappropriate treatment.
- Standard thyroid function tests may not always be definitive in cases of hyperthyroxinemia.
Observation:
- A patient and family members presented with elevated total thyroxine (T4) levels.
- Thyroid-stimulating hormone (TSH) levels were not suppressed, and free T4 (FT4) and free T4 index (FT4I) were normal.
- Triiodothyronine resin uptake (T3RU) levels were low.
Findings:
- These atypical results suggested an underlying issue with thyroid hormone transport rather than overproduction.
- Measurement of serum thyroid-binding globulin (TBG) levels revealed familial hepatic overproduction of TBG.
- Family-wide testing confirmed the diagnosis of euthyroid hyperthyroxinemia due to inherited TBG excess.
Implications:
- Accurate diagnosis of benign familial hyperthyroxinemia prevents unnecessary medical interventions for thyrotoxicosis.
- Understanding TBG levels is critical in interpreting thyroid function tests in certain populations.
- Genetic counseling and family screening are important for inherited thyroid hormone transport abnormalities.