When they draw your blood titer they will not be testing your epitestosterone vs testosterone ratio nor will they be testing for any specific compounds. That being said, you should be sure to find out if they are only drawing a blood titer. Also, one thing to consider is the ability of PH/AAS to affect your immune system (think test flu) and how that may interfere with the titer results. Will they know you are on PH/AAS? No. Will it possibly skew the titer results? Possible.
If you can avoid it, that would be optimal, but realistically would I be worried about "popping" for steroids, no.