They're ready for you, doctor/Doctor

I know that "Doctor" is capitalized when their name follows, like Dr. Watson/Doctor Watson, but what about when addressing a doctor without mentioning their name?

They're ready for you now, doctor.

vs

They're ready for you now, Doctor.

Without the name, the title should be in lowercase.

I'm quoting from the Chicago Manual of Style, 13th ed.

(Section 7.17) In text matter, titles following a personal name or used alone in place of a name are, with few exceptions, lowercased.

Without the doctor's name, you should say:

They're ready for you now, doctor.

You are correct in your example of Doctor Watson.

(Section 7.15) Civil, military, and professional titles and titles of nobility are capitalized when they immediately precede a personal name, as part of the name.

If you were to use the doctor's name, you should say:

They're ready for you now, Doctor House.