Importance of maintaining species homology in thyroid hormone radioimmunoassays: modification of 'human' radioimmunoassay kits for use with rat samples.

Lack of species homology in radioimmunoassays can lead to serious errors. We have shown that a highly significant bias results from application of commercially available 'human' thyroxine and triiodothyronine assays to rat samples. This paper describes a simple modification whereby this source of error is overcome. Validation of the modified assays demonstrated their high degree of reliability.