Interference of anti-T3 autoantibodies in the measurement of total and free T3 in serum

Abstract

A case of anti-tdlodothyronine sutoantibodies is presented in this report. The thyroid hormone profile of a hypertensive patient, with multinodular goiter and history of exogenous thyroid hormone therapy, was found to be highly ambiguous. The total as well as free T3 levels were consistently high (out of range) whereas the T4 (total and flee) values were always within normal limits. The thyrotropin was found to be partially suppressed. Very low T3-Uptake indicated some kind of interference in the immunoassays. We incubated the sera with the radio-iodine labelled T3 and observed that the patient's serum bound about ten times more radioactivity than a control run in parallel. On further resolving the serum proteins on cellulose acetate electrophoresis, the radioactivity was detected in the y-globulin band. Therefore it was established that the patient's serum carried the antibodies reactive with T3 which were interfering in the immunoassays. Elevated anti-thyroid microsomal antibodies were also present in the patient's serum. The anti-T3 antibodies were highly specific for T3 and did not show any cross reactivity with the T4 or its analogues used in the estimation of free T4.

False Elevation of Free Thyroxine and Triiodothyronine Due to the Presence of Antibodies to Iodothyronines

“…Erregragui et al reported that autoantibodies against the hormone-forming site included in P3 peptide of thyroglobuline (12). Depending on the immunometric method being used these antibodies can result in free and total iodothyronine levels that are falsely high or low (4,5,6,7,13). In our patient, this led to the suspicion of TSH producing adenoma, RTH and resistance to TSH, all having been excluded by specific tests.…”

Interference of anti-T4 autoantibodies in the single step free T4 radioimmunoassays

“…The extremely high levels of serum FT4 in this patient can be explained by the presence of some interfering agent which appeared to compete with the antibodies used in the radioimmunoassay. The autoantibodies against thyroid hormones interfering in the RIA have been reported (3,4,8), but the binder reacting with radiolabelled T4 resulting in its precipitation could be any other serum protein also. The increased affinity/capacity of different plasma proteins particularly albumin has been reported as in familial dys-albuminemic hyperthyroidism(11).…”

“…Circulating antibodies to various thyroid antigens like thyroperoxidase, thyroglobulin, thyrotropin receptors and microsomal proteins may be found in various autoimmune thyroid disorders (1). Sometimes the autoantibodies may be generated against the thyroid hormones themselves (2,3,4). The incidence of anti-T3 or anti-T4 antibodies with varied specificity and dissociation constants in a euthyroid healthy population is about 1.8% (5).…”

“…The incidence of anti-T3 or anti-T4 antibodies with varied specificity and dissociation constants in a euthyroid healthy population is about 1.8% (5). The presence of these antibodies interferes with the estimation of total and free hormones by single step immuno assay (3,4,5,6) and may result in very low (undetectable) values (in competitive RIA/EIA that uses precipitation for the separation of bound and free ligand) or spuriously high values (in immunoassays using antibody coated tubes) of either or both T3 and T4 (7,8). The antibodies in…”

Laboratory and clinical features of abnormal macroenzymes found in human sera

“…Unfortunately, that is not fully understood at present. However, immune complexes with numerous serum bioactive substances have been also reported in recent years [135,[196][197][198][199][200][201][202][203][204][205][206][207][208]. For example, blood coagulation factor, various hormones (triiodothyroxine, thyroxine, chorionic gonadotropin, pituitary hormones and so on), vitamin B12, myocardial markers and so on complexed with immunoglobulin.…”