Tests for bowel cancer

General tests

Physical examination

Your doctor will ask to feel your abdomen for any swelling. To check for problems in the rectum and anus, they may also do an internal examination. The doctor puts a gloved, lubricated finger into the anus to feel for any lumps or swelling. This is called a digital rectal examination (DRE). If you feel embarrassed or scared about a DRE, let your doctor know. A nurse may be present, but you can also ask for a family member or friend to be in the room with you for support.

The DRE may be uncomfortable, but it shouldn’t be painful. Because the anus is a muscle, it can help to try to relax during the examination. The pressure on the rectum might make you feel like you are going to have a bowel movement, but it is very unlikely that this will happen.

Blood test

You may have a blood test to check your general health and look for signs that you are losing blood from your bowel. The blood test may measure chemicals from your liver and check your red blood cell count (haemoglobin level). Having low red blood cells (anaemia) is common with bowel cancer, but it may also be caused by other conditions.

Checking your faeces (poo) for signs of blood

A test called the immunochemical faecal occult blood test (iFOBT) looks for tiny amounts of blood in your faeces. It is commonly used as a screening test for bowel cancer.

An iFOBT is generally not recommended for people who are bleeding from the rectum or have other bowel symptoms (e.g. a change in bowel habit, anaemia, unexplained weight loss, abdominal pain). People with these symptoms are usually referred for a colonoscopy straightaway.

For an iFOBT, you usually collect a sample of your faeces at home. The sample is sent to a laboratory and examined for traces of blood, which may be a sign of polyps, cancer or another condition. Only a small number (around 3–4%) of positive iFOBT tests are due to cancer or large precancerous polyps; more commonly the traces of blood are from benign conditions like haemorrhoids. However, if the test finds blood in your faeces, your doctor will recommend you have a colonoscopy (see below).

Colonoscopy, polypectomy and biopsy

Colonoscopy

This is the main test to look for bowel cancer. It lets your doctor look at the  lining of the entire large bowel. Before a colonoscopy, you clear out the bowel with a preparation. It’s very important to follow the instructions – the cleaner the bowel, the more likely it is that the doctor can see polyps or areas of concern.

Most colonoscopies are done as day surgery at a hospital. On the day of the procedure, you will usually be given a sedative or light anaesthetic so you don’t feel anything. This will make you drowsy or may put you to sleep. A colonoscopy usually takes 20–30 minutes.

During the procedure, the doctor puts a colonoscope (a flexible tube with a camera on the end) through your anus and up into the rectum and colon. Carbon dioxide or air is passed through the colonoscope to inflate the colon and make it easier for the doctor to see the bowel.

Polypectomy

During the colonoscopy, any precancerous polyps will be removed – this is called a  polypectomy. Most polyps are small (less than 1 cm) and the procedure is very safe and usually has no side effects.

Biopsy

If the doctor sees abnormal-looking areas, including polyps, they will remove a sample of the tissue. This is called a biopsy. A pathologist looks at the sample under a microscope to check for cancer or specific gene changes (see Genomic testing).

Side effects

You may be weak or drowsy so someone will need to take you home afterwards. You won’t be able to drive until the day after your procedure. The gas used to inflate the bowel can sometimes cause bloating or wind pain. Rare complications include bleeding, or damage to the bowel (perforation) or spleen. Your doctor will explain the risks.

Less commonly used tests

CT colonography

Also called a virtual colonoscopy, it uses a CT scanner to create images of the colon and rectum. Bowel preparation is usually needed before the test. A CT colonography is done by a radiologist (who analyses x-rays and scans).

You may have a CT colonography if a colonoscopy didn’t show all of the colon or when a colonoscopy is not safe. However, a CT colonography is not often used because it exposes you to radiation and is not as accurate as a colonoscopy. It can see only bigger polyps, not small ones.

If any abnormality is detected, you will need to have a colonoscopy so that the doctor can take tissue samples. A CT colonography is covered by Medicare only in limited circumstances.

Flexible sigmoidoscopy

This test is similar to a colonoscopy but only lets the doctor see the rectum and about the lower half of the colon (sigmoid and descending colon). Before a flexible sigmoidoscopy, you will need to have a light bowel clean-out, usually with an enema. You may be given light sedation for the procedure.

You will then lie on your left side while a colonoscope (or, sometimes, a shorter but similar tube called a sigmoidoscope) is put into your anus and guided up through the bowel. The colonoscope or sigmoidoscope blows carbon dioxide or air into the bowel to inflate it slightly so the doctor can see the bowel wall more clearly.

A light and camera at the end of the colonoscope or sigmoidoscope show up any unusual areas or polyps, and your doctor can take tissue samples (biopsies).

Further tests

If tests show you have bowel cancer, more tests will be done to see if it has spread to other parts of your body. Before you book any test, ask how much it will cost.

CEA blood test

You may be tested for carcinoembryonic antigen (CEA), a protein produced by some (not all) bowel cancers. Low levels are normal – but if you have a high level, your doctor may do more tests. Smoking, pregnancy and other factors can also raise CEA levels. If CEA is high, it will be retested after treatment to see if it has returned to normal.

CT scan

A CT (computerised tomography) scan uses x-rays and a computer to create a detailed picture of the inside of the body. CT scans are usually done at a hospital or radiology clinic.

A dye is injected into a vein to make the pictures clearer. It may make you feel hot, have a strange taste in your mouth or feel that you need to urinate (wee or pee), but these sensations won’t last long.

During the scan, you lie still on a table that moves in and out of the machine. Your chest, abdomen and the area between your hip bones (pelvis) will be scanned to see if the cancer has spread to these areas. The scan itself takes 5–10 minutes and is painless.

MRI scan

An MRI (magnetic resonance imaging) scan uses a powerful magnet and radio waves to create detailed pictures of the inside of your body. MRIs are mostly used only for cancers in the rectum, not cancers higher in the bowel. An MRI may also be used to scan the liver if there was an abnormality seen on a CT scan that needs to be checked.

Before the scan, let your medical team know if you have a pacemaker or any other metallic object in your body. If you do, you may not be able to have an MRI scan as the magnet can interfere with some metallic objects. Newer devices are often safe to go into the scanner.

Before the MRI, you may be injected with a dye to help make the pictures clearer. During the scan, you lie on a table that slides into a large metal tube open at both ends. The noisy, narrow machine makes some people feel anxious or claustrophobic. If you might feel distressed, talk to your medical team beforehand. You may be given medicine to help you relax. You will wear headphones or earplugs. The scan may take 30–90 minutes, depending on the area being scanned.

PET–CT scan

A positron emission tomography (PET) scan combined with a CT scan is a specialised imaging test. The 2 scans provide more detailed and accurate information about the cancer. A PET–CT scan is most commonly used before surgery to help find out where the cancer has spread to in the body. It can also be used after surgery to check if the cancer has come back after treatment.

When you make the appointment for the scan, you will be given instructions to follow about how to prepare for the scan, including what you can eat and drink.

Before the scan, you will be injected with a glucose solution containing a small amount of radioactive material. Cancer cells show up brighter on the scan because they take up more glucose solution than the normal cells do. You will then be asked to sit very quietly or lie down for 30–90 minutes as the glucose spreads through your body. Then you will have the scan itself, which usually takes around 30 minutes.

You will also usually have a CT scan, before or after the PET scan.

Medicare will only cover the cost of a PET–CT scan for bowel cancer in limited circumstances. If this test is recommended, check with yourdoctor what you will have to pay.

Bowel preparation

Before some tests, you will have to empty your bowel completely so the doctor can see the bowel clearly. This is called bowel preparation (or washout) and can vary, so ask your doctor what you need to do. It’s important to follow the instructions so you don’t have to repeat the test.