Surveillance colonoscopy vs. screening and diagnostic colonoscopies

I understand the difference between screening services (exam for seemingly healthy individuals with no sign or symptom of disease, using V76.51) and diagnostic services (exam to determine the cause of a particular symptom). While patients don't always like to hear that their exam is diagnostic and not screening, we seem to have a policy in place to defend our refusal to bill diagnostic exams as screening...

Now the issue of "surveillance" exams has come up. A particular patient has Crohn's disease (555.2), he has dealt with symptoms of this disease for many, many years. He has had colonoscopies about every two years to monitor the disease. In plain black and white, his colonoscopy reports (from his previous doctors) state "surveillance colonoscopy". As far as I know, he's never had any polyps.

Patient is adamant about us billing as a screening exam (as its paid 100% by insurance). I called his insurance and they told me he's entitled to one screening colonoscopy every single year (isn't that odd? EVERY YEAR?) Anyway, I explained the patient's ongoing symptoms and they said he would not qualify for a screening exam. But, the "surveillance" issue has me thinking. Is "surveillance" billed the same as screening or diagnostic or does it have its own codes?