Diagnosing colorectal cancer usually begins with a visit to your family doctor. Your doctor will ask you about any symptoms you have and may do a physical exam. Based on this information, your doctor may refer you to a specialist or order tests to check for colorectal cancer or other health problems.
The process of diagnosis may seem long and frustrating. It’s normal to worry, but try to remember that other health conditions can cause similar symptoms as colorectal cancer. It’s important for the healthcare team to rule out other reasons for a health problem before making a diagnosis of colorectal cancer.
The following tests are commonly used to rule out or diagnose colorectal cancer. Many of the same tests used to diagnose cancer are used to find out the stage, which is how far the cancer has progressed. Your doctor may also order other tests to check your general health and to help plan your treatment.
Your health history is a record of your symptoms, risk factors and all the medical events and problems you have had in the past. In taking a health history, your doctor will ask questions about a personal history of:
Your doctor may also ask about a family history of:
A physical exam allows your doctor to look for any signs of colorectal cancer. During a physical exam, your doctor may:
Find out more about physical exam.
A CBC measures the number and quality of white blood cells, red blood cells and platelets. A CBC is done to check for anemia from long-term (chronic) bleeding.
Find out more about complete blood count (CBC).
Blood chemistry tests measure certain chemicals in the blood. They show how well certain organs are functioning and can help find abnormalities.
Liver function tests measure how well the liver is working. Higher levels of certain substances may mean that colorectal cancer has spread to the liver.
Find out more about blood chemistry tests.
Stool tests check for hidden, or occult, blood in the stool. A guaiac-based fecal occult blood test (gFOBT) or a fecal immunochemical test (FIT) may be done during diagnosis if it was not used during screening.
Find out more about screening for colorectal cancer, including stool tests.
A double-contrast barium enema is an imaging test that uses a special substance (barium sulphate) and x-rays to make images of the entire large intestine (cecum, colon, rectum and anus). Air is pumped into the intestine to improve the view.
A double-contrast barium enema may be done when there is a positive fecal occult blood test (FOBT). It is also done if you have symptoms of colorectal cancer, such as bleeding from the rectum, blood in the stool or abdominal pain. It can show polyps or growths in the colon.
Find out more about barium enema.
Sigmoidoscopy is a procedure that uses a thin, tube-like instrument with a light and lens on the end (called an endoscope). It is used to look at the sigmoid colon (the last part of the colon) and rectum. A biopsy can be done during the sigmoidoscopy.
The type of endoscope used for this procedure is called a sigmoidoscope. Doctors generally use flexible sigmoidoscopes because they give more complete views of the sigmoid colon and are more comfortable than rigid sigmoidoscopes.
A flexible sigmoidoscopy may be done if you have symptoms of colorectal cancer, such as changes in bowel habits, blood in the stool or abdominal pain.
A rigid or flexible sigmoidoscopy may be done to measure the distance a rectal tumour is from the anus. Tumours that are lower in the rectum and close to the anus may need radiation therapy before surgery.
Find out more about sigmoidoscopy.
Colonoscopy is the main test used to diagnose colorectal cancer. During a colonoscopy, the doctor looks inside the colon and rectum using a flexible tube with a light and lens on the end. This tool is called a colonoscope.
A colonoscopy is done if you have blood in your stool or other symptoms of colorectal cancer. It is also used to check polyps or other abnormal areas that were found during a double-contrast barium enema or sigmoidoscopy. The doctor may also collect a biopsy sample during colonoscopy.
Find out more about colonoscopy.
During a biopsy, the doctor removes tissues or cells from the body so they can be tested in a lab. The report from the lab will confirm whether or not cancer cells are present in the sample.
A biopsy is usually done during a colonoscopy or sigmoidoscopy to remove polyps (called polypectomy) or small amounts of tissue from the colon or rectum. This may be called an endoscopic biopsy.
A core biopsy may be used to collect samples from organs where the cancer may have spread, such as the liver.
Find out more about biopsy.
Cells and tissues can be studied in the laboratory to look for the presence or effects of cancer. They can also look for certain changes or characteristics in the body. Cells may be collected from blood or urine. They can also come from tissue samples collected with biopsy or other procedures. Find out more about cell and tissue studies.
The following cell and tissue studies may be done for colorectal cancer.
Carcinoembryonic antigen (CEA) is a tumour markertumour markerA substance in the body that may indicate the presence of a certain type of cancer.. Doctors usually measure CEA before surgery to set a starting point, or baseline, that they can use to check future levels. Measuring CEA levels is usually done as a part of follow-up. CEA levels that are higher than the baseline may mean the cancer is not responding to treatment or has come back (recurred). Find out more about carcinoembryonic antigen (CEA).
KRAS is a gene that can be mutated, or changed, in some colorectal cancer cells. The KRAS test is usually done on colorectal tumours in people with metastatic colorectal cancer because it may show if targeted therapy is a treatment option. Colorectal tumours that test positive for the KRAS gene mutation are unlikely to respond to the targeted therapy drugs such as cetuximab (Erbitux) and panitumumab (Vectibix). Colorectal tumours that don’t have the KRAS gene mutation are called KRAS wild-type tumours.
Microsatellite instability (MSI) is a change to the genetic material, or DNA, in a cell. Normally, mismatch repair (MMR) genes correct any mistakes to DNA that happen when it’s copied during cell division. When the MMR genes don’t work properly, MSI can happen. People with Lynch syndrome have a mutation in one of their MMR genes. Doctors may test biopsy samples from a colorectal tumour for MSI to find out if the tumour could have been caused by Lynch syndrome.
DRE is an exam in which the doctor inserts a gloved finger into the rectum to check for lumps or swelling. It is usually done as part of a physical exam. DRE is also done to measure how far a rectal tumour is from the anus. Tumours that are lower in the rectum and close to the anus may need radiation therapy or chemoradiation before surgery.
DRE is used with a transrectal ultrasound or pelvic MRI to find out the stage of the rectal cancer, including how deep the tumour has grown into the wall of the rectum.
Find out more about digital rectal exam (DRE).
A computed tomography (CT) scan uses special x-ray equipment to make 3-D and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures.
A CT scan is used to check if colorectal cancer has spread to lymph nodes or organs in the chest, abdomen and pelvis. It is usually done before surgery to create a starting point, or baseline, that doctors can compare to CT scans done after surgery during follow-up.
A CT scan of the pelvis may be used to measure how far a rectal tumour is from the anus. Tumours that are lower in the rectum and close to the anus may need radiation therapy or chemoradiation before surgery.
Doctors can also use a CT scan to guide a biopsy needle to a specific area in the body. This is called a CT-guided biopsy. It is used to check if colorectal cancer has spread to certain organs, such as the liver.
A virtual colonoscopy, also called a CT colonography, uses special equipment to make images of the colon and rectum without using an endoscope. It looks for polyps and cancer. Researchers are still studying virtual colonoscopy to see if it is effective in diagnosing colorectal cancer. If virtual colonoscopy equipment is available, you may be offered this test if you can’t have a regular colonoscopy.
Find out more about CT scan.
Ultrasound uses high-frequency sound waves to make images of structures in the body. It may be used to check if colorectal cancer has spread to the liver.
Transrectal ultrasound (TRUS) is also called endorectal ultrasound. TRUS is an ultrasound technique in which the ultrasound transducer, or probe, is placed inside the rectum. It is used to find out the stage of the rectal cancer, including how deep the tumour has grown into the wall of the rectum. TRUS may also be used to measure how far a rectal tumour is from the anus. Tumours that are lower in the rectum and close to the anus may need radiation therapy or chemoradiation before surgery.
Magnetic resonance imaging (MRI) uses powerful magnetic forces and radiofrequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3-D pictures.
MRI of the pelvis may be used to find out the stage of rectal cancer and where cancer has spread within the pelvis, such as to the lymph nodes. It may also be used to measure how far a rectal tumour is from the anus. Tumours that are lower in the rectum and close to the anus may need radiation therapy or chemoradiation before surgery.
Find out more about MRI.
An x-ray uses small doses of radiation to make an image of the body’s structures on film. A chest x-ray is used to check if colorectal cancer has spread to the lungs.
Find out more about x-ray.
A positron emission tomography (PET) scan uses radioactive materials called radiopharmaceuticals to look for changes in the metabolic activity of body tissues. A computer analyzes the radioactive patterns and makes 3-D colour images of the area being scanned.
A PET-CT scan combines images from a PET scan and a CT scan, which are done at the same time using the same machine. It may be used to help with staging colorectal cancer or plan surgery for metastatic tumours.