No blood test can diagnose this disease. The only way is via a colonoscopy. However, your GP may order kidney and liver function tests sent to a pathology laboratory to check your overall health. There is also a blood test for a chemical sometimes produced by colon cancers.
The bottom line here is that although many symptoms such as inflammatory bowel disease, and ulcerative colitis are common in other conditions.  If you have a personal history and you're worried, never accept an explanation that says you are too young to have cancer. You may have familial adenomatous polyposis (Lynch syndrome) so ask your doctor for a referral for another test or further investigation.  If you receive a positive result and it's found early, it can be treated.
Bowel cancer can metastasis into breast cancer, lung cancer or another common cancer and if you have a strong family history, a first degree relative or one second degree relative, get a test and ask for a colonoscopy even if you are younger, or an earlier age than the screening program allows.   Cancer Council Australia has set guidelines for the diagnosis and treatment of colorectal cancer.