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Evaluation of thyroid function in patients with thyroid hormone autoantibodies
1Third Department of Internal Medicine, Gifu University School of Medicine, Japan.
Clinica Chimica Acta; International Journal of Clinical Chemistry
|October 15, 1993
Summary
Thyroid hormone autoantibodies in Hashimoto's and Graves' disease do not affect thyroid function. Accurate free thyroxine (FT4) measurements are possible using equilibrium dialysis or analog assays after polyethylene glycol (PEG) treatment.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Immunology
Background:
- Thyroid hormone autoantibodies can interfere with standard free thyroxine (FT4) assays.
- Accurate assessment of thyroid function is crucial in autoimmune thyroid diseases like Hashimoto's thyroiditis and Graves' disease.
Purpose of the Study:
- To evaluate the accuracy of FT4 measurements in patients with thyroid hormone autoantibodies.
- To determine if FT4 assays require modification in the presence of these autoantibodies.
Main Methods:
- Measured serum FT4 using equilibrium dialysis/radioimmunoassay and analog radioimmunoassays.
- Treated sera with polyethylene glycol (PEG) to remove autoantibodies before re-measurement.
- Assessed serum thyrotropin (TSH) levels before and after TRH stimulation.
Main Results:
- Analog FT4 assays yielded falsely high values without treatment.
- FT4 values measured by equilibrium dialysis were compatible with basal TSH.
- PEG treatment of sera normalized FT4 values in analog assays, correlating well with equilibrium dialysis results (r=0.98).
Conclusions:
- Real FT4 levels in patients with thyroid hormone autoantibodies are consistent with basal TSH.
- Thyroid hormone autoantibodies do not inherently disrupt the hypothalamo-pituitary-thyroid axis regulation.
- Equilibrium dialysis or PEG-treated analog assays provide valid FT4 measurements for assessing thyroid function in these patients.