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Primary hypothyroidism with paradoxically elevated plasma thyroxine due to thyroxine-binding antibody.
Postgraduate Medical Journal
|September 1, 1986
Summary
This study details a case of hypothyroidism misdiagnosed due to thyroid hormone antibodies interfering with radio-immunoassay tests. Sensitive TSH assays helped resolve diagnostic challenges and guide treatment.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Immunology
Background:
- Hypothyroidism diagnosis typically relies on thyroid hormone levels and TSH.
- Assay interference can complicate accurate diagnosis and treatment monitoring.
Observation:
- An elderly patient presented with clinical hypothyroidism, showing low T3 but paradoxically high TT4 and fT4 by RIA.
- Primary hypothyroidism was confirmed by elevated TSH and low fT4 using a different assay method.
Findings:
- Thyroid hormone antibodies specifically bound T4, interfering with RIA measurements and causing falsely elevated TT4 and fT4 levels.
- The interference complicated initial diagnosis and assessment of thyroid hormone replacement therapy.
Implications:
- Accurate thyroid function testing requires awareness of potential antibody interference.
- Sensitive immunoradiometric TSH assays are valuable tools for resolving diagnostic ambiguities in such cases.