Are you referring to a Prothrombin Time test to check blood clotting times? If so that's not a thyroid test and wouldn't be something we'd be familiar with... You can get more information on that test in the General Health community, which can be accessed via the following link:
http://www.medhelp.org/forums/General-Health/show/164
If your question is thyroid related, please be more specific as to the test that was done...