I know this study is from 1998 so may be old information - apologies if this has been posted before. There are more up to date articles about this and from the uk but this one had much more information:
I remember reading that the TSH test has been improved so am not sure if that is related to this. Does anyone know? If this is still current, then it's another factor against the reliability of thyroid function tests and a strong argument for antibody testing.