Funny you should ask. I turned 50 years old in 2000 and my internist recommended that I have a screening colonoscopy to establish a baseline. Since I had an AVR the previous year, I had to decide whether to take the test at all, take it while on Coumadin or stop the Coumadin, go into the hospital, wean off the Coumadin and onto Heperin, then have the test before being put back on the Coumadin. I discussed this with my gastroenterologist and we decided that I would take the test while on the Coumadin since there was no family history of colon cancer and this was for screening purposes only. The odds were vastly in my favor that no polyps would be found.
Of course they found a polyp. This necessitated going home, weaning off the Coumadin - my INR dropped from 3.0 on a Tuesday to 1.4 that Friday. The polyp was removed on Friday - STAT - since I was in danger of developing a clot at that INR level. After the removal, I was admitted to the hospital and put on a Heparin drip and put back on the Coumadin. I was scheduled to be released on Monday - after 3 days in the hospital.
I hemoraged on that Sunday, while in the hospital, and began bleeding from the polyp removal site. This worsened over the next few days and my blood count dropped. Finally, I had another procedure on the following Tuesday where the polyp removal site was re-cauterized to stop the bleeding. To make a long story short, the polyp turned out to be pre-cancerous and I will need another colonoscopy at the end of this year. We will do that one while on Coumadin and roll the dice that they won't find anything that needs removal since only 2 years will have elapsed.
All of that said, had I not had the screening test, I would have had a polyp that would have become cancerous. Given all the Coumadin related stuff that happened after the procedure, I still had a very dangerous situation corrected even if it meant alot of inconvenience and discomfort. The alternative would have been much worse had I developed colon cancer.
My suggestion is to have the test. Since they already found a polyp once - even a benign one, you can't ignore this and not be tested. Whether to roll the dice and do it on Coumadin and hope that they don't find anything or stop the Coumadin in case they need to remove something is your decision. The odds are with me that they won't find another polyp so soon. If they do, it will be the same drill as last year.
With regards to how often to have the test. If your polyp was not pre-cancerous, you can safely extend the test intervals. If suspect, as mine was, you need to be checked more frequently - every 18 to 24 months in my case. Given the consequences of not finding a polyp, I'm going to be retested. With regards to being tested on Comadin or off, I would suggest that since you have a history of having polyps and since if they find one, they will need to remove it, I'd try it on Coumadin if done soon and off Coumadin if you extend the intervals.
Hope this makes sense and helps you decide.
I had a colonoscopy 3 years ago at which time they removed a polyp and told me then to come back in 3 years. In the meantime I had an appt. with the gastro doc and he said there was no need for a recheck. That goes against everything I've read. My question is how do they handle the coumadin issue for this type of test? Does it mean a stay in the hospital? UGH! I've developed this aversion to hospitals since my 3 stints with the heart surgery two years ago! 
