The procedure notes that I have seen where the physician is using 45390 has been incorrect. After a great deal of research with another CPC, we discovered that each of these patients actually had a 45385 and 45381. The patient received a saline injection with snare polypectomy. The physicians have been choosing 45390 which is a mucosal resection and was not correct for the procedure performed. You may want to closely review the actual procedure note to see if this is the case for you. 45385 and 45381 can both receive a 33 modifier if the original diagnosis code was Z12.11 and the patient is not Medicare.
Hope this helps.