
Originally Posted by
Maetenloch
Since testosterone and it's metabolites are naturally occuring substances, all they can do is compare the ratio of test to other compounds that are produced along with it. One of these, epitestosterone, is produced typically in a 1-to-1 ratio with testosterone. If you're taking exogenous test, you'll have high test levels but low epitestosterone levels. If the ratio is greater than 6-1, they assume that your test levels are artificially raised.
Of course one way around this is to also inject epitestosterone along with your test to keep the ratio down. Epitest is available underground and some professional athletes use it just for this reason. Currently the only way to detect this is to look at the carbon isotopes in the epitestosterone which will indicate whether it was produced in living tissue or synthesized.