Without knowing the situation, it is difficult to say. How is the company as a whole? What are the company policies that could affect you?
You could handle it by asking for information rather than making a blunt announcement. Perhaps you don't know the answers and are going to HR to ask about company policies, insurance coverage, etc. That way, you haven't committed by saying "I am"; instead, you are asking how this affects someone who is considering transition.
Hope this helps.