Bowel Cancer UK

You may have some tests when you visit your GP. Other tests are done in hospital. Bowel cancer may also be diagnosed through a screening programme

Some people are diagnosed after going into hospital in an emergency with pain in the stomach area and sickness (vomiting). 

Most people with bowel cancer are diagnosed when they are over the age of 50. But more than 2,500 people under 50 are diagnosed each year in the UK.

American Cancer Society

If you have symptoms that might be from colorectal cancer, or if a screening test shows something abnormal, your doctor will recommend one or more of the exams and tests below to find the cause.

Medical history and physical exam

Your doctor will ask about your medical history to learn about possible risk factors, including your family history. You will also be asked if you’re having any symptoms and, if so, when they started and how long you’ve had them.

As part of a physical exam, your doctor will feel your abdomen for masses or enlarged organs, and also examine the rest of your body. You may also have a digital rectal exam (DRE). During this test, the doctor inserts a lubricated, gloved finger into your rectum to feel for any abnormal areas.

Tests to look for blood in your stool

If you are seeing the doctor because of anemia or symptoms you are having (other than obvious bleeding from your rectum or blood in your stools), he or she may recommend a stool test to check for blood that isn’t visible to the naked eye (occult blood), which might be a sign of cancer. These types of tests – a fecal occult blood test (FOBT) or fecal immunochemical test (FIT) – are done at home, and require you to collect 1 to 3 samples of stool from a bowel movement. For more on how these tests are done, see Colorectal Cancer Screening Tests.

(A stool blood test should not be the next test done if you’ve already had an abnormal screening test, in which case you should have a diagnostic colonoscopy, which is described below.)

Blood tests

Your doctor might also order certain blood tests to help determine if you have colorectal cancer. These tests also can be used to help monitor your disease if you’ve been diagnosed with cancer.

Complete blood count (CBC): This test measures the different types of cells in your blood. It can show if you have anemia (too few red blood cells). Some people with colorectal cancer become anemic because the tumor has been bleeding for a long time.

Liver enzymes: You may also have a blood test to check your liver function, because colorectal cancer can spread to the liver.

Tumor markers: Colorectal cancer cells sometimes make substances called tumor markers that can be found in the blood. The most common tumor marker for colorectal cancer is carcinoembryonic antigen (CEA).

Blood tests for this tumor marker can sometimes suggest someone might have colorectal cancer, but they can’t be used alone to screen for or diagnose cancer. This is because tumor marker levels can sometimes be normal in someone who has cancer and can be abnormal for reasons other than cancer.

Tumor marker tests are used most often along with other tests to monitor patients who have already been diagnosed with colorectal cancer. They may help show how well treatment is working or provide an early warning that a cancer has returned.

Diagnostic colonoscopy

A diagnostic colonoscopy is just like a screening colonoscopy, but it's done because a person is having symptoms, or because something abnormal was found on another type of screening test.

For this test, the doctor looks at the entire length of the colon and rectum with a colonoscope, a thin, flexible, lighted tube with a small video camera on the end. It is inserted through the anus and into the rectum and the colon. Special instruments can be passed through the colonoscope to biopsy or remove any suspicious-looking areas such as polyps, if needed.

Colonoscopy may be done in a hospital outpatient department, in a clinic, or in a doctor’s office.


This test may be done if rectal cancer is suspected. For this test, the doctor looks inside the rectum with a proctoscope, a thin, rigid, lighted tube with a small video camera on the end. It’s put in through the anus. The doctor can look closely at the inside lining of the rectum through the scope. The tumor can be seen, measured, and its exact location can be determined. For instance, the doctor can see how close the tumor is to the sphincter muscles that control the passing of stool.


Usually if a suspected colorectal cancer is found by any screening or diagnostic test, it is biopsied during a colonoscopy. In a biopsy, the doctor removes a small piece of tissue with a special instrument passed through the scope. Less often, part of the colon may need to be surgically removed to make the diagnosis. See Testing Biopsy and Cytology Specimens for Cancer to learn more about the types of biopsies, how the tissue is used in the lab to diagnose cancer, and what the results may show.

Lab tests of biopsy samples

Biopsy samples (from colonoscopy or surgery) are sent to the lab where they are looked at closely. .If cancer is found, other lab tests may also be done on the biopsy samples to help better classify the cancer and possibly find specific treatment options.


Gene tests: If the cancer has spread (metastasized), doctors will probably look for specific gene changes in the cancer cells that might help determine which drugs will be more helpful in treatment than others. For example, doctors now typically test the cancer cells for changes in the KRAS, NRAS, and BRAF genes. Patients whose cancers have mutations in these genes typically do not benefit from treatment with certain targeted therapy drugs. In the case of tumors that have the BRAF V600E mutation, they are not only less likely to respond to certain targeted drugs, but may need a different type of targeted drug added for treatment to work.


MSI and MMR testing: Colorectal cancer cells are typically tested to see if they show high levels of gene changes called microsatellite instability (MSI). Testing might also be done to see if the cancer cells have changes in any of the mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2). EPCAM, another gene related to MSH2, is also routinely checked with the 4 MMR genes. 

Changes in MSI or in MMR genes (or both) are often seen in people with Lynch syndrome (HNPCC). Most colorectal cancers do not have high levels of MSI or changes in MMR genes. But most colorectal cancers that are linked to Lynch syndrome do.

There are 2 possible reasons to test colorectal cancers for MSI or for MMR gene changes:

  • To identify patients who should be tested for Lynch syndrome. A diagnosis of Lynch syndrome can help schedule other cancer screenings for the patient (for example, women with Lynch syndrome may need to be screened for endometrial cancer). Also, if a patient has Lynch syndrome, their relatives could also have it, and may want to be tested for it.

  • To determine treatment options for colorectal cancer.

Imaging tests to look for colorectal cancer

Imaging tests use sound waves, x-rays, magnetic fields, or radioactive substances to create pictures of the inside of your body. Imaging tests may be done for a number of reasons, such as:

  • To look at suspicious areas that might be cancer

  • To learn how far cancer might have spread

  • To help determine if treatment is working

  • To look for signs of cancer coming back after treatment

Computed tomography (CT or CAT) scan

CT scan uses x-rays to make detailed cross-sectional images of your body. This test can help tell if colorectal cancer has spread to nearby lymph nodes or to your liver, lungs, or other organs.

CT-guided needle biopsy: If a liver or lung biopsy is needed to check for cancer spread, this test can also be used to guide a biopsy needle into the mass (lump) to get a tissue sample to check for cancer.


Ultrasound uses sound waves and their echoes to create images of the inside of the body. A small microphone-like instrument called a transducer gives off sound waves and picks up the echoes as they bounce off organs. The echoes are converted by a computer into an image on a screen.

Abdominal ultrasound: For this exam, a technician moves the transducer along the skin over your abdomen. This type of ultrasound can be used to look for tumors in your liver, gallbladder, pancreas, or elsewhere in your abdomen, but it can't look for tumors of the colon or rectum.


Endorectal ultrasound: This test uses a special transducer that is inserted into the rectum. It is used to see how far through the rectal wall a cancer has grown and whether it has reached nearby organs or lymph nodes.


Intraoperative ultrasound: This exam is done during surgery. The transducer is placed directly against the surface of the liver, making this test very useful for detecting the spread of colorectal cancer to the liver. This allows the surgeon to biopsy the tumor, if one is found, while the patient is asleep.




Every year over 2,500 younger people are diagnosed with bowel cancer in the UK


If you think you have reason to believe you may have bowel cancer, engage with your health professionals and insist that your concerns are dealt with without delay.