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Thyroid hormone binding protein abnormalities in patients referred for thyroid disorders
S V Bhatkar1, M G R Rajan, A Velumani
1Laboratory Nuclear Medicine Section, Bhabha Atomic Research Centre, Mumbai, India.
The Indian Journal of Medical Research
|October 19, 2004
Summary
Thyroid hormone binding protein (THBP) abnormalities can cause discrepancies in thyroid function tests. Screening for these abnormalities, particularly thyroxine-binding globulin (TBG) variations, is crucial for accurate diagnosis and treatment, especially in families with inherited conditions.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Genetics
Background:
- Thyroid hormone binding protein (THBP) abnormalities are a primary cause of discordant thyroid function tests (TFTs).
- These abnormalities do not affect thyroid hormone action but can complicate interpretation of standard tests like total thyroxine (T4) and thyrotropin (TSH).
- Accurate identification of THBP abnormalities is vital for correct thyroid function assessment, especially when free T4 (FT4) assays are unavailable.
Purpose of the Study:
- To analyze the prevalence of THBP abnormalities in patients attending a thyroid clinic.
- To investigate the inheritance patterns of quantitative thyroxine-binding globulin (TBG) abnormalities within affected families.
Main Methods:
- Screening of 15,000 consecutive patients over four years (1994-1997) for thyroid function.
- THBP abnormalities were detected using polyacrylamide gel electrophoresis autoradiography.
- Serum TBG, total T4, free T4, and total tri-iodothyronine (TT3) levels were measured using radioimmunoassay.
Main Results:
- The study identified complete and partial TBG deficiency at rates of 1:2,500 and 1:200, respectively.
- TBG excess was found at a rate of 1:15,000.
- Family studies revealed X-chromosome linked inheritance for TBG deficiency in two families and TBG excess in one family.
Conclusions:
- It is recommended to screen for THBP abnormalities before interpreting TFTs, especially when T4 and TSH levels show significant discrepancies.
- Screening family members of individuals with inherited THBP abnormalities is essential to prevent misdiagnosis and inappropriate treatment of future thyroid dysfunction.