EVALUATION OF THYROID-FUNCTION IN PATIENTS WITH THYROID-HORMONE AUTOANTIBODIES

Serum free thyroxine (FT4) levels were measured in patients with Hashi moto's thyroiditis and Graves' disease who were seropositive for thyro id hormone autoantibodies. The methods used were equilibrium dialysis/ radioimmunoassay (FT4 by equilibrium dialysis, Nichols Institute) and FT4 analog radioimmunoassay (Amerlex MFT4) before and after treatment of sera with 12.5% polyethylene glycol (PEG). Furthermore, FT4 measure ment in the PEG-treated sera was done using two other analog radioimmu noassays (DPC FT4 kit and N-FT4 Corning). Serum thyrotropin (TSH) conc entration before and after i.v. infusion of thyrotropin releasing horm one (TRH) was measured in five cases of Hashimoto's thyroiditis and fo ur cases of Graves' disease with thyroid hormone autoantibodies. Altho ugh FT4 determination by analog tracer radioimmunoassays showed unusua lly high values for the hormone, results obtained by an equilibrium di alysis/radioimmunoassay method showed compatible values with basal TSH . Furthermore, FT4 concentrations measured with Amerlex MFT4 after tre atment of sera with 12.5% PEG, correlated well with the values obtaine d by equilibrium dialysis/radioimmunoassay (r = 0.98, P < 0.001). Simi lar results were obtained with two other analog FT4 radioimmunoassays after treatment of sera with PEG. These results indicate that real FT4 values in patients with thyroid hormone autoantibodies are compatible with basal TSH concentrations. The presence of thyroid hormone autoan tibodies per se does not affect the control mechanism of the hypothala mo-pituitary-thyroid axis. It was concluded that measurement of basal TSH as well as FT4 values by either equilibrium dialysis/radioimmunoas say or analog radioimmunoassays after PEG treatment provides clinician s with valid information for assessment of the precise status of thyro id function in patients with thyroid hormone autoantibodies.