Can a FIT test detect bowel cancer?

Faecal immunochemical tests (FIT) are designed to detect blood in stool, which can be an early sign of bowel cancer. At an early stage, bowel cancer may only produce very tiny amounts of blood that can’t be seen. A FIT test helps detect these blood traces in the stool.

Bowel cancer is the 4^th commonest cancer in the UK¹. Unfortunately, many of the symptoms of bowel cancer are not noticeable until the cancer reaches an advanced stage.

Thinking about bowel cancer and getting tested can feel uncomfortable, but early detection saves lives. At Selph, gut health is one of our areas of expertise.

In this article, we will discuss everything you need to know about FIT tests, including:

• What a FIT test is
• How a FIT test works
• The accuracy of FIT tests
• What a positive FIT test means and what the next steps are
• Who can or should take a FIT test
• How to get hold of a FIT test

What is a FIT test?

A FIT or qFIT (quantitative faecal immunochemical test, to give its full name) test uses a small stool sample to check for tiny amounts of blood in the stool. It's quick, painless and can be done at home.

The FIT test kit helps you easily take a stool sample and preserve it for testing. The sample can then be posted to or dropped off at a clinic or hospital laboratory, where it can detect traces of blood.

How does a FIT test work?

A FIT test can detect microscopic amounts of blood in the stool using an “antibody”. Antibodies are proteins the immune system makes that bind to specific targets (usually viruses and bacteria). In the FIT test, the antibodies have been designed to bind to human globin, a part of blood cells.

Once your sample reaches the laboratory, scientists add a solution containing these globin antibodies. If the globin is present, the antibodies bind to it and this binding is detected by specialised lab equipment. The more globin there is in the sample, the stronger the reaction, indicating a higher level of blood.

This specificity of the qFIT test for globin is important for two reasons. Firstly, by only binding to human globin, a qFIT test will only detect your blood. You can't get a positive qFIT result eating red meat. Secondly, the globin protein is broken down by enzymes in the small bowel. Once the globin is broken down, it can't be detected by the qFIT test. This means that a positive qFIT result will tend to indicate bleeding in the large bowel (colon) rather than from higher up where it would be digested. However, qFIT test can sometimes be positive even with bleeding from the stomach or small bowel but it's not as common.

How accurate is a FIT test?

A FIT test is very accurate in detecting blood in stool. Many scientific studies in recent years have proven this. One study showed that a negative FIT test (i.e., no blood seen in the stool sample) means an almost zero chance of having bowel cancer².

The scientific evidence is so strong that FIT tests are now the starting point for bowel cancer screening throughout the world. So, if your FIT test is negative, you can be almost certain that you don’t have bowel cancer.

But no single test is perfect. A very small number of people with a negative FIT test might have bowel cancer - roughly 1 in 1000. If your FIT test is negative, you should still see a doctor if you are experiencing any bowel symptoms.

Does a positive FIT test mean bowel cancer?

A positive FIT test doesn’t always mean bowel cancer. In fact, most people who have a positive FIT test won’t have bowel cancer.

Remember, the FIT test is looking for blood in the stool. Blood in the stool can be caused by bowel cancer, but many non-cancerous conditions can also cause bleeding.

Common non-cancerous conditions that cause blood in the stool include:

• Haemorrhoids
• Anal fissure
• Gastroenteritis
• Diverticular disease
• Inflammatory bowel disease (IBD, which is different to IBS)

These conditions will still require diagnosis treatment, and monitoring. Therefore, it is important to act early if you have a positive FIT test or any other symptoms.

A positive FIT test can be daunting and cause a lot of anxiety. You’ll get advice about the next steps if you have a positive test. If you’ve tested positive, you might be seen by your GP or go straight to see the specialist in hospital. Generally speaking, most people will need a colonoscopy. This procedure involves placing a thin, flexible tube with a camera on the end into the colon to look for any cancers or non-cancerous conditions that are causing blood in the stool.

These arrangements can be made very quickly. Even though it can be daunting, acting soon is essential if you have a positive FIT test. It might help to talk to a trusted relative or friend, and ask if they can accompany you to further appointments.

Remember, most people with a positive FIT test don’t have bowel cancer and early action is best.

Can anyone take a FIT Test?

Yes, anyone can take a FIT test but there are two main groups of people who should be testing.

Firstly, anyone with bowel symptoms who's 40 and older should take a FIT test to check for bowel cancer. The National Institute for Health and Care Excellence (NICE) recommends that GPs arrange a qFIT test before referral for symptoms such as weight loss, a change in bowel habit, bleeding from the bottom or stomach pain.

Secondly, everyone should be screening for bowel cancer with a FIT test every year from age 45 at the latest. There is a national bowel cancer screening programme but it only starts at 50 and only tests every other year. It also has some major deficiencies regarding what FIT result is considered "positive". You can read more about the problems with the NHS bowel cancer screening programme in our article.

Age is the major risk-factor for developing bowel cancer but other things that might put you at increased risk of bowel cancer are:

• Family history
• Diagnosis of inflammatory bowel disease (IBD)
• Smoking
• Obesity
• Diet high in alcohol, sugar and processed meat
• Diet lacking in fibre

So, if you have any of these factors, it is definitely worth taking a FIT test if you develop any of the symptoms described.

How can I get a FIT Test?

There are a few different ways to get a FIT test. If you are aged between 50 and 74 years, you will automatically be sent a FIT test through the NHS bowel cancer screening programme every 2 years.

Alternatively, if you have bowel symptoms, you can book an appointment with your GP.

If you want to do a FIT before the age of 50 and either don't have bowel symptoms or don't want to wait for a GP appointment, you can also get a FIT test from us. We'll send you the kit with next-day delivery and you'll usually get your results the same day as the lab receives the sample. The FIT analysis is identical to what you would receive from your GP as the lab also tests NHS samples. We also make a donation to St Mark’s Hospital Foundation with every test.

Worried about bowel cancer? Take our qFIT test.