Nandrolone metabolites would be in your systems for up to 18 months, so you could test positive that you took it. But metabolites are different than having hyperelevated levels of nandrolone in your body from currently taking it in supraphysiological doses. I'm having a brain fart rightnow, and cant remember what deca would do to other markers/blood levels other than testosterone/epitest. Do you know what he's going to test for?
So I'll give this a bump, and see if someone else can give you more direct experience and commentary wrt to what nandrolone would elevate, and if your doctor would know if you were on more than his HRT script.
Good luck