Anti-triiodothyronine autoantibodies interfere with two recently commercialized radioimmunoassays for free triiodothyronine.

We examined the effect of anti-triiodothyronine autoantibodies on results of RIA of free triiodothyronine with two commercial kits (Amersham International and Diagnostic Products Corp.). Both methods gave falsely high results because the 125I-labeled analogs used in these RIAs were bound by the autoantibodies.