I just had a colonoscopy this year it came out fine. my doc. did a blood test last month and it came back positive. could i get cancer that fast?

Uh, wait...: No blood test is diagnostic for colon cancer. Possibly your CEA was a bit high but that proves nothing if you're not a smoker; otherwise i must assume there is a misunderstanding. Life's tough enough without having a worry like this one. Any doubts, get a second opinion.

Unlikely: But there are a lot of reasons for blood in the stool. Certainly colonoscopy is not 100% as well. I am sure your doctor is working through the possible causes.

What test?: There is no blood test for colon ca. Cea can be a marker for colon ca as well as many other conditions, including benign (not cancer). Can't diagnose colon ca just by using cea; can help monitoring colon cancer patients once a diagnosis has been made, i.e. Biopsy proved mass. Colonoscopy is best test, but not perfect-can have a miss rate of abnormalities, including polyps and cancer.