The visit prior to a screening colonoscopy for a healthy patient is not billable
Scenario 1:
If patient comes in with no symptoms and they just need to have a screening for either preventive age 50+ once every 10 years or high risk (i.e. personal hx, family hx, etc), then you cannot bill an E/M. There is nothing to evaluate and manage. In most cases the patients are being sent by a PCP to have the procedure. The PCP already determined they needed it. All your MD is doing is going over their H&P, discussing risks & benfits, and scheduling. This is pre-op work weather the pateint follows through or not.
Scenario 2:
If patient comes in with sign and symptoms, your MD has to perform an evaluation and managent visit to determine the plan of care which includes the treatment and/or diagnostic studies (i.e. colonoscopy). You should bill with the appopriate E/M with the appropriate sign/symptom/diagnosis.