Interesting thread. I'm an old school, old lady who's worked in allied health field forever (no MD after my name).

I've always from day one in my career used formal titles for MD/PhD/DO people until invited to do otherwise. Mostly out of respect, but also because I believe people get to choose how they prefer to be addressed. Just me. I HATE when someone decides to rename a Susan as Suzy, or Daniel as Danny!

Two pdocs in my life I've called Dr. Last name.....and never been invited to use a first name. Which is fine, just write me the correct medication and dosage, thank you kindly!

I followed pattern with my current and only T into the second year of our sessions. One day, she casually said, ya know, you're my only client who calls me Dr. Jones.
Well, who knew?
So that's how she became Mary.
Kinda silly that she didn't mention she prefers first name earlier, I think......