Technically they cant dent you. But, if you go in and ask for things like prolactin, E2, TT and the likes of that stuff be preparred for questions. Because those arent 'regular bloodwork items' for monitoring health as far as theyre concerned.
The issue most guys have about admitting to steroid use to their Dr. is the fact that they live in the USA and admitting to something like that can fuck things up in the future when it comes time to buy medical insurance, you will considered 'higher risk'.
Here in Canada it is different. It the LAW to provide every Canadian citizen with medical care no matter what. They CAN NOT take that away from you no matter what.