Here's what I go by found from Medicare and one other site from Surg Strategies- not sure what insurance your patient has... Hope this helps.
INCOMPLETE COLONOSCOPIES
An incomplete colonoscopy is one in which the physician is unable to pass the scope past the splenic flexure. This may happen because of various reasons including a poor prep. CPT guidelines state “for an incomplete colonoscopy, with full preparation for a colonoscopy, use a colonoscopy code with modifier -52 and provide documentation.”
However, Medicare's guidelines state to use modifier -53 in this situation. Failure to use modifier -53 will result in a denial (because of frequency limitations) when the patient returns for their repeat colonoscopy next week or next month.
Incomplete Colonoscopies
For coding purposes, the colonoscope must pass the splenic flexure. If this is not achieved, it is an incomplete colonoscopy. In these instances, you should use the CPT code for the procedure intended and append one of the following modifiers:
Modifier 73—Discontinued procedure due to extenuating circumstances or those threatening the well being of the patient prior to the administration of anesthesia. The physician may cancel or discontinue the procedure subsequent to the patient's surgical preparation (including sedation, and being taken to the room where the procedure is to be performed).
Modifier 74—Discontinued procedure due to extenuating circumstances or those threatening the well being of the patient after the administration of anesthesia, or after the procedure was started.
When using these modifiers, it is important to have supporting documentation that clearly states how far the scope was inserted and the reason for the discontinuation. This information should be sent with the claim form for proper reimbursement.