People who experience rectal bleeding along with a change in their bowel habits are 1.8 times more likely to have colorectal cancer compared to those without these symptoms, which helps doctors decide when further testing is needed.

We analyzed the available evidence and found that when rectal bleeding and a change in bowel habits occur together, the likelihood of colorectal cancer increases. Specifically, people with both symptoms are 1.8 times more likely to have colorectal cancer compared to those without these symptoms [1]. This pattern helps guide doctors in deciding whether further testing is warranted. What we’ve found so far is based on 39.0 supporting assertions and no refuting evidence. The number 1.8 represents a likelihood ratio — meaning, for every person without these symptoms who has colorectal cancer, about 1.8 people with both symptoms have it. This doesn’t mean these symptoms always mean cancer, but they do make it more common in that group. We don’t know how often these symptoms appear in people without cancer, or how many people with cancer don’t have these symptoms. The evidence doesn’t tell us if age, family history, or other factors change this ratio. It also doesn’t say whether one symptom alone carries the same weight. The evidence we’ve reviewed leans toward using this combination of symptoms as a signal for further evaluation, but it doesn’t confirm cancer is present. It simply shows a stronger association when both symptoms happen together. If you notice blood in your stool along with a lasting change in how often or how you go to the bathroom, it’s worth talking to a doctor — not because it’s definitely cancer, but because it’s a sign that checks are needed.