I always get a chuckle when I read about suggested replies by gun owners: "None of your business." Well....that's almost the same as a "Yes" answer. Someone who doesn't own guns wouldn't be annoyed at the question; they'd just answer: "No, I don't have guns in my home." And, if they happen to be anti gun, they'd be proud to say they don't own a gun.
"Why are you asking?" or "What does that have to do with my visit?" Same thing; it would be an irrelevant question to non gun owners & they would just say "No, I don't have guns in my home."
You really have only two choices: Lie & say "No," or just say "Yes." If the doctor is filling out a form, he will probably write your answer on the form & anyone reading it will find it as amusing as I do.
I have 2 spray guns. Does that count? My wife has a glue gun.
Due to NYS pistol permit regulations, they already know I own firearms. My doctor doesn't ask. My dentist is a hunter and we talk about guns all the time during a visit. Most everyone I know owns 1 or more firearms. Most are hunters. But in reality it is a dumb question unless your doctor is a psychiatrist.