A complete colonoscopy according to Current Procedural Terminology published by the AMA is:

“Colonoscopy, flexible, proximal to the splenic flexure; diagnostic, with or without collection of specimen(s) by brushing or washing, with or without colon decompression (separate procedure)”

According to Medicare guidelines, a reduced services modifier is warranted only if you are not able to advance beyond the splenic flexure. Therefore a colonoscopy is considered complete if you have reached this point of the colon.

Some physicians feel that unless they get to the cecum, this is an "imcomplete" colonoscopy and want to append a reduced modifier -52 to the procedure code. However this would be incorrect. Only if the physician is unable to advance beyond the splenic flexure, would you consider this incomplete.    picture courtesy of http://202.129.54.82/faculty/web_bed/apichat/digestive/page/large-intestine.html