ANSWER: Screening for a disease means the person has no symptoms. Since you now have rectal bleeding, a colonoscopy would be considered not a screening test, but a diagnostic test.
Whether you have it now or wait to see if more bleeding occurs depends upon many factors. The most important question is whether anything found on the colonoscopy will lead to treatment that improves your quality of life.
It comes down to two points: If you are actively bleeding and it can’t be controlled, then you probably should have the colonoscopy to try to stop the bleeding. The continued bleeding would make you weak and might require transfusions.
If the bleeding was minimal and has stopped, you and your doctor should discuss the pros and cons of colonoscopy. For instance, would you want to know if there is a polyp or cancer? Would you wish to have it treated if one is found?