Concentrations of free thyroxin and free triiodothyronine in serum of patients with thyroxin- and triiodothyronine-binding autoantibodies

Abstract

Between 1982 and 1989 we identified 47 subjects with spuriously increased concentrations of free thyroxin (FT4) or free triiodothyronine (FT3) related to autoantibody interference in analog FT4 and (or) FT3 methods. The incidence of autoantibody interference observed during one year (1988) was 1 in 2460. In the subjects identified, 51% and 11%, respectively, showed an increased binding of radiolabeled T4 or T3 analog alone; 38% had an increased binding of both. Of 36 patients tested, 71% had autoantibodies to thyroglobulin and microsomal fraction of the thyroid, 19% to microsomal fraction alone, and 9.5% to thyroglobulin alone. In eight subjects, spuriously increased FT4 concentrations were reported with the following FT4 methods (in decreasing order of interference): Coat-A-Count, Amerlex-M, Amerlite, Seria, Magic Lite, Amerlex-MAB. In the same eight subjects, Amerlex-M and Seria reported spuriously increased concentrations of FT3.

Autoimmune Abnormalities of Postpartum Thyroid Diseases

“…Only two of the three women had PPT. Previously, the same group ( 79 ) found that the rate of THAb, as estimated by the interference (overestimation) of FT4 and/or FT3 by the Amerlex analog method, was 0.04% (1/2460), 50-fold less than the above 2.0%.…”

Autoantibodies against Thyroid Hormones Can Lead to an Erroneous Diagnosis and Potentially Harmful Treatment

“…Since thyroid hormone autoantibodies were first reported, there have been reports of their existence in patients with a variety of thyroid disorders like primary hypothyroidism, hyperthyroidism, carcinoma, goitre and nonthyroid autoimmune conditions.e" Their frequency is as high as 64% among patients with biochemical thyroid results contradictory with clinical status" and the incidence of autoantibody interference in analogue FT4 and/or FT3 measurement has been estimated to be one in 2460. 7 They have also been reported in up to 1•8% healthy Japanese subjects, although in this case they do not seem to influence the measurement of thyroid hormones." The detection of thyroid autoantibodies is more efficient with methods using thyroid hormone analogues'i?…”

Thyroid function tests, incongruent internally and with thyroid status, both in a pregnant woman and in her newborn daughter

“…In particular, thyroglobulin epitopes for THAb can be identified at positions 20–190, 1277–1314 and 2403–2768 as recently described ( 15 ). Although the prevalence of THAb in the general population is low (from less than 1.0 to 1.8%) ( 16 , 17 , 18 ), they are more frequent in patients with autoimmune diseases, in particular with autoimmune thyroid disease ( 18 , 19 ). However, this frequency may be underestimated because THAb are not routinely evaluated and they are often transient in serum.…”