Quote Originally Posted by Bron
The testosterone made in the body has a higher ratio of carbon-13 in it than testosterone made in a lab. A mass spectrometer can be used to measure the ratio of C-13 to C-12.

There is a summary of this on cyclingnews.com:
http://www.cyclingnews.com/news.php?...terone_testing

Bron
Great article, Bron, thanks. This makes it all clear to me.. At least the premise... now for the results!