Autoantibodies to thyroid hormones: association with falsely low hormone levels measured by 'Amerlex' assay.

Autoantibodies to thyroxine (T4) and tri-iodothyronine (T3) were found in a 21-yr-old thyrotoxic woman who had paradoxically low T4 and T3 as measured in the 'Amerlex' solid phase radio-immunoassay. Though rare, thyroid hormone antibodies should be suspected if anomalous thyroid function results are obtained and alternate assay procedures used.