Diagnosis based only on patient history

A new patient, 23 years old, presents to clinic needing an "approval letter" to take her dogs on the airplane with her. Her husband accompanies her and states she has "high-functioning autism" and is fearful of flying, so she needs her dogs with her. They bring no documentation, and as this is a new patient, there are no established diagnoses in her chart. Husband does state he could provide documentation of her having autism from high school records, but he doesn't have it with him today. Two dogs also accompany her to the visit.

Patient not examined.

Dx: Autistic disorder by history, 299.00.

Plan: Companion animal letter created for patient. Obtain records from previous PCP.

Would you pick up the provider's stated dx of autism or perhaps phobia, 300.29? Either way, it's based on what the patient says. Is that enough?

I guess my bottom-line question is whether we can code per patient history only when there is no exam or testing done to confirm. And once again, I ask if what the provider states as the diagnosis is what I should go with (rather than coding symptoms).

Thanks for your help!

Diagnosis based only on patient history