Colonoscopy

A colonoscopy is an examination of your rectum (back passage) and large intestine (large bowel).

It involves passing a thin, flexible, telescope-like tube with a light and a camera on the end (a colonoscope) via your anus into your large bowel. This allows your doctor to see the inner lining of your rectum and large intestine to check for any abnormal changes.

During a colonoscopy, tissue samples (biopsies) may also be collected by passing small instruments through the colonoscope.

Signs of needing a colonoscopy

Your doctor may recommend a colonoscopy to investigate bowel-related symptoms, to check the state of a pre-existing bowel condition or as part of bowel cancer screening.

Common symptoms investigated via colonoscopy

If you experience any of the symptoms below, your GP may refer you for a colonoscopy:

Abdominal pain

Abdominal pain is usually investigated with a colonoscopy if it is also accompanied by other bowel-related symptoms, such as rectal bleeding, constipation or diarrhoea.

Persistent abdominal pain or frequent episodes of abdominal pain can be caused by a variety of bowel conditions. This includes:

• Bowel cancer
• Constipation
• Duodenal and stomach ulcers
• Gastritis
• Inflammatory bowel disease ie Crohn’s disease and ulcerative colitis
• Irritable bowel syndrome (IBS)

However, abdominal pain can also be caused by conditions that do not involve the bowel, such as recurrent urinary tract infections and, in women, period pain and endometriosis.

Chronic (long-term) constipation

Bowel habits vary between individuals; however, if you are passing stools less often than usual, you are straining to pass stools and/or they are hard and lumpy, you most likely have constipation. If this persists for 3 months or more, it is chronic constipation.

The most common causes of constipation are related to diet and lifestyle, such as:

• A diet low in fibre
• A change in your diet or taking a new medication
• A sedentary lifestyle – spending most of your time sitting or being inactive, with very little physical activity
• Anxiety, stress and/or depression
• Not drinking enough fluids
• Not opening your bowels when you have the urge

However, in rare cases, chronic constipation may be caused by a bowel condition, such as bowel cancer or diverticular disease. A colonoscopy can help diagnose these conditions.

Chronic (long-term) diarrhoea

Diarrhoea refers to passing looser, runnier stools than is normal for you. Diarrhoea often causes you to pass stools more often than usual. If this persists for at least 4 weeks, it is chronic diarrhoea. 
Most people experience diarrhoea at some point in their life, usually due to a bowel infection (gastroenteritis) caused by eating food contaminated with bacteria, viruses or parasites.

However, chronic diarrhoea is usually caused either by eating or drinking something in excess that your bowel is sensitive to or by a bowel condition, such as coeliac disease, diverticular disease, irritable bowel syndrome or inflammatory bowel disease.

Iron-deficiency anaemia

If you have frequent headaches, fatigue, shortness of breath, paler skin and/or heart palpitations, your doctor may recommend you have a blood test to check for iron-deficiency anaemia.

Depending on your medical history and any other symptoms, you may be referred for further tests, such as a colonoscopy. This is because iron-deficiency anaemia can be caused by persistent, slow blood loss due to bleeding in your large bowel — this can be investigated via a colonoscopy.

Rectal bleeding

You may notice blood in your stools or blood on the tissue when wiping your anus after opening your bowels. Piles (haemorrhoids) and anal fissures are common causes of rectal bleeding and can usually be diagnosed without a colonoscopy. However, a colonoscopy can help diagnose other causes of rectal bleeding, including:

• Bowel cancer
• Diverticular disease
• Inflammatory bowel disease ie Crohn’s disease and ulcerative colitis
• Stomach and duodenal ulcers

Bowel cancer screening

As part of the UK National Bowel Cancer Screening Programme, adults aged 50–75 years are offered an at-home screening test for bowel cancer. This involves the collection of a stool sample and is called a faecal immunochemical test (FIT).

The stool sample is sent off to a lab for examination and is checked for signs of blood in your stools. If blood is detected, you will need further tests, which may include a colonoscopy. 

Bowel conditions monitored via colonoscopy

If you have been diagnosed with a bowel condition, you may have a colonoscopy at regular intervals or if your condition flares up to check the health of your bowel.

Bowel conditions that are often monitored via colonoscopy include inflammatory bowel disease (Crohn’s disease and ulcerative colitis) and small growths in the bowel called polyps.

If you have had polyps removed, your doctor will recommend a colonoscopy to check if any new polyps have developed.

Is a colonoscopy right for you?

If you have unexplained bowel-related symptoms, it’s important to see your doctor for further investigations. This will help rule out serious health conditions, such as bowel cancer, which is the fourth most common type of cancer in the UK.

A colonoscopy provides a thorough visual examination of the lining of your large bowel and the opportunity to collect tissue samples for further examination. It, therefore, helps your doctor diagnose potential bowel conditions so that you can receive appropriate treatment. 

However, a colonoscopy is not suitable if you have a severe health problem, such as a severe heart or lung condition or bleeding disorder.

Alternative treatments to a colonoscopy

Some bowel-related conditions, such as an anal fissure, do not need a colonoscopy and can be investigated using a proctoscope. This is a short, rigid tube with a camera and a light on the end that is inserted via your anus into your rectum. It is used to visually examine the anus and rectum.

If a visual examination of the entire large bowel is needed but a colonoscopy is not suitable, your doctor may recommend a virtual colonoscopy. This is where a CT scan is used to create detailed images of the inside of your bowel. It is, therefore, also known as CT colonography or a CT cologram.

Unlike a standard colonoscopy, no tissue samples can be collected during a virtual colonoscopy.

A colonoscopy involves inserting a thin, flexible, telescope-like tube with a light and a camera on the end (colonoscope) via your anus into your rectum. It is then guided up into your large intestine. Live images of the inside of your rectum and large intestine are transmitted to a screen so your doctor can look for any abnormalities.

If an area of abnormal tissue is identified, your doctor may collect a tissue sample during your colonoscopy by passing small instruments through the colonoscope. In some cases, small polyps can also be removed during a colonoscopy.

How to prepare for a colonoscopy

Before your colonoscopy, you will be asked to fill in a questionnaire about your medical history. Depending on your answers, you may need to attend a clinic to be reviewed by a specialist nurse.

They will let you know whether you need to temporarily stop taking certain medications before your procedure. For example, if you take iron tablets, you will need to stop taking them in the week running up to your colonoscopy. Your nurse will also explain whether you need to have any other tests (eg blood tests) before your colonoscopy. 

The day before your colonoscopy, you will be given strong laxatives to help empty your bowels. The laxatives are usually provided as a powder that you dissolve in water and drink. It is recommended that you stay home after taking the laxatives as you will need to open your bowels frequently.

You will receive instructions on which foods and drinks you should avoid the day before your colonoscopy. You will also be told when to stop eating and drinking anything other than clear fluids (ie how long to fast for).

On the day of your colonoscopy

Before your colonoscopy, your personal and medical details will be checked, and you may have some basic tests performed, such as checking your pulse, blood pressure and temperature.

You will also be asked to sign an informed consent form and to change into a hospital gown and disposable underwear.

Who will be involved?

Your colonoscopy will be performed by a specialist doctor called an endoscopist with the support of a specialist nurse.

How long does a colonoscopy take?

A colonoscopy takes 20–30 minutes; however, your entire appointment may last up to 2 hours.

Anaesthesia

A colonoscopy is not performed under anaesthesia. However, as the procedure can be uncomfortable, you will be given painkillers and a sedative via a small tube inserted into a vein in your arm (intravenous drip).

The sedative will make you feel sleepy and relaxed but will not put you to sleep. However, you are still unlikely to remember much about your procedure after it is over.

If you have a sedative, you will not be able to drive or operate heavy machinery for the next 24 hours.

You may also be offered gas and air, which is known as laughing gas or Entonox. This can be used in addition to or instead of a sedative and makes you feel relaxed. It is breathed in via a mask placed over your mouth and nose. Unlike a sedative administered directly into your bloodstream, gas and air wear off quickly, within a few minutes.

What happens during a colonoscopy?

Throughout your procedure, your blood pressure, heart rate and oxygen levels will be measured via small monitoring devices. After you have been given painkillers and a sedative, you will be asked to lie on your left side with your legs bent.

First, your doctor will gently examine your rectum by inserting a gloved finger into your anus. Then, some lubricating gel will be applied and the colonoscope carefully inserted. Air or carbon dioxide gas will be pumped via the colonoscope into your bowel to inflate it. This allows your doctor to get a clearer view of the lining of your large bowel.

Live images will be sent from the camera at the end of the colonoscope to a screen. Your doctor will examine your large bowel to check for any abnormalities. In some cases, tissue samples will be collected via special instruments passed through the colonoscope. Small polyps can also be removed this way.

What happens straight after a colonoscopy?

Once your colonoscopy is complete, the colonoscope will be carefully removed, and you will be transferred to a recovery room.

Your blood pressure, heart rate and oxygen levels will continue to be monitored closely.

In most cases, a colonoscopy is a day case, which means once the sedation has worn off enough, you will be allowed to go home.

Your colonoscopy results

In most cases, before you return home, your doctor will discuss your colonoscopy results with you. They will let you know if your results are normal, that is, no growths (polyps) or signs of cancer or other bowel diseases, or if they found abnormalities, collected tissue samples and/or removed any polyps.

If abnormalities are found, your doctor will let you know when to expect further results from any tissue samples collected and whether you need any additional tests. Once your diagnosis is confirmed, they will also explain your treatment options.

A report containing your results will be sent to the doctor who referred you for your colonoscopy, such as your GP or private consultant.

If you have a sedative, you should not drive home after your colonoscopy. Instead, you should arrange for someone to accompany you and stay with you until the effects of the sedative completely wear off, which can last up to 24 hours. The sedative may make you feel nauseous for up to 24 hours.

You may also feel some slight discomfort, cramping and bloating for several hours after your procedure. This is due to the air or carbon dioxide gas that was pumped into your bowel. It will gradually pass out of your body, but you can help speed up this process by walking around, massaging your abdomen, passing wind and going to the toilet.

You can also take over-the-counter painkillers as instructed by your care team to help with any discomfort. 

If you have a biopsy or polyps removed, you may notice a little blood in your stools the first time you open your bowels after your colonoscopy.

You can eat and drink as normal after a colonoscopy and can return to your usual activities, including work, the next day.

Every procedure comes with risks; however, a colonoscopy is generally considered to be a low-risk procedure if you do not have any pre-existing severe health conditions, such as a heart or lung condition or bleeding disorder.

In a few cases in every 1,000, a colonoscopy can cause mild rectal bleeding if a biopsy was performed or polyps were removed. There is also a low risk — a few in every 1,000 cases — of a colonoscopy causing a tear in the bowel. This is more likely if a biopsy is collected or a polyp removed, and may need surgery to repair it.

In very rare cases, an allergic reaction to the sedative occurs. This is why you will be closely monitored immediately after your procedure until the effects of the sedative have worn off enough.

As no test is completely accurate, there is a risk of a colonoscopy missing an abnormality. This occurs in a few cases in every 100. There is an equal risk of your colonoscopy not being completed due to difficulties viewing the entire large bowel. If this occurs, you may need further tests or another colonoscopy.