Antibody Binding of Thyroid Hormone in Juvenile Goitrous Hypothyroidism

Abstract

Serum thyroxine (T₄) and triiodothyronine (T₃) concentrations by RIA were undetectable in a 14 year old hypothyroid girl who had goiter. Hormone dysgenesis was suspected in this patient and she was treated with T₄. Although the clinical hypothyroid state improved towards normal, T₄ and T₃ values by RIA were consistently low. To clarify the discrepancy between laboratory and clinical diagnosis, T₄ concentration in serum was determined by non-RIA competitive protein displacement assay in the ethanol extract of the patient's serum. The value noted was 12.6 µg/100 ml and was consistent with the euthyroid state of T₄ treated patient. Prompted by these findings, the patient's serum was further subjected to serologic and electrophoretic analysis for screening anomalous T₄ binding proteins. A T₄ binding immunoglobulin in patient's serum was detected, while the serologic tests revealed a low thyroglobulin antibody titer. The antibody had high specificity for T₄ but not for T₃ and other thyroid analogues as noted in inhibition experiments. The electrophoretic observations demonstrating gamma globulinthyroxine interaction were consistent with that noted in an RIA system (using barbital and ANS) where antibody-tracer thyroxine binding curves were examined at various dilutions of patient's serum. The gradually increasing frequency of reports demonstrating gamma globulin interaction of thyroid hormone in thyroid diseases, stresses the need for setting up appropriate thyroid hormone assay controls to detect anomalous T₄ and T₃ binding proteins in serum in order to avoid erroneous laboratory and clinical diagnosis.

Key words

Thyroid Hormone Antibody Interference in RIA of T₄ and T₃ - Thyroid Hormone Antibodies in Goitrous Hypothyroidism - Thyroid Hormone Antibodies in Juvenile Lymphocytic Thyroiditis