None of your business doc. If I’m ever asked. Never have been yet.
I would probably give him a lecture on the constitution if pressed further.
The other thing I refuse to give is my SS#. I tell them ‘not in this day of identity theft’. And they haven’t press it yet.
I actually walked out of a doctor’s office when the secretary insisted I provide my SSN. Told her no and that I was reporting the doctor to my insurer for violation of the privacy act.