What tests are used to diagnose bowel cancer?

When it comes to suspected bowel cancer, time is of the essence – which is why Cromwell Hospital endeavours to provide a swift, streamlined service through our bowel care diagnostic pathway. Upon entering the pathway, you can expect a thorough and comprehensive assessment of your condition by one of our world-class consultants, followed by a series of diagnostic tests tailored to your symptoms.  

What is bowel cancer?

Bowel cancer, also known as colorectal cancer, is a general term that refers to cancers beginning in the large bowel.

Your bowel can be divided into two parts: the small bowel and the large bowel. The large bowel contains your colon, back passage (rectum) and bowel opening (anus). The term ‘bowel cancer’ usually refers only to colon cancer and rectal cancer.

As with other types of cancer, bowel cancer develops when abnormal cells begin to grow and divide out of control. Bowel cancer can spread (metastasise) to other parts of the body.

In the UK, bowel cancer is the fourth most common type of cancer with over 30,000 cases per year, and the second most fatal. Fortunately, many cases of bowel cancer can be successfully treated if caught early – which is why it's essential to be aware of any warning signs.

Bowel cancer symptoms

There are several symptoms of bowel cancer that you should look out for:

  • Blood or mucus in your stool (poo)
  • Changes in bowel habit, e.g. passing stools more or less often
  • Lower abdominal pain, bloating or discomfort after eating
  • Loss of appetite
  • Unexplained weight loss
  • A persistent feeling of needing to empty your back passage
  • Tiredness and breathlessness, usually as a result of anaemia

Bowel cancer tests

Based on your symptoms, you may be recommended one or more of the following diagnostic procedures:


An endoscopy is a type of diagnostic procedure that provides a better look inside different parts of your body. There are two types of endoscopy commonly used for diagnosing bowel cancer: colonoscopy and flexible sigmoidoscopy.

Most endoscopies are carried out without sedation. If you are particularly nervous about your endoscopy, you can choose to have sedation so that you are asleep throughout the procedure.

Occasionally, your consultant may take a small tissue sample (biopsy) during your procedure for further examination at a laboratory.


A colonoscopy is one of the most common diagnostic tests used for bowel cancer. It’s a type of endoscopy, which is used to examine your large bowel (rectum and colon). A long, thin telescopic tube, called a colonoscope, is passed through your back passage (rectum) to gain entry to your large bowel. 

A colonoscopy is recommended for patients experiencing symptoms like rectal bleeding, anaemia, persistent diarrhoea, and changes in bowel habit. 

Flexible sigmoidoscopy 

A flexible sigmoidoscopy is a type of endoscopy used to examine your sigmoid colon (the lower part of your bowels).  

The procedure uses an instrument called a sigmoidoscope, which is a long, flexible and tube-like telescopic camera. The sigmoidoscope is passed into the lower bowels through your back passage.

Capsule endoscopy

A capsule endoscopy is a different to other endoscopies that use thin, tube-like instruments to visualise inside the body.

As its name suggests, this procedure involves swallowing a small capsule (about the size of a vitamin tablet), which contains a wireless camera. This capsule passes through the bowels, taking pictures as it goes. These pictures are transmitted to a small computer which is worn around the waist, like a belt.

Once the capsule is swallowed, you are free to go about your normal activities. The capsule is disposable and will exit the body naturally and painlessly through your bowel movements. This is usually used to examine the small bowel, which is not reachable with conventional endoscopy.

Endoscopic ultrasound

An endoscopic ultrasound (EUS) combines an endoscopy procedure with ultrasound technology to produce images that are greater in detail than those achieved through a standard ultrasound.

Similar to an endoscopy, a thin, tube-like instrument called an endoscope is inserted through the back passage. However, this type of endoscope also has a small ultrasound transmitter in the tip, which produces images from inside the large bowel using high-frequency soundwaves. 

If you are anxious about having an endoscopic ultrasound, you may choose to be sedated so you're asleep throughout the procedure.

MRI scan

An magnetic resonance imaging (MRI) scan is a diagnostic imaging procedure that uses strong magnetic fields and radio waves to produce images from inside your body. It can be used to detect tumours and other abnormalities within the bowels. 

CT scan

A computer tomography (CT) scan is an imaging procedure that uses X-ray beams and computer software to produce detailed images from inside your body. It is also known as a CAT scan.  

In cases of suspected bowel cancer, a CT scan helps screen for tumours or other abnormalities within the lower gastrointestinal system.  

Blood tests

Blood tests can be used to look for the presence of tumour markers, which may be an indication of cancer. Blood tests alone cannot be used to diagnose bowel cancer.

Tumour markers are substances (usually proteins) that are created by the body in response to cancer growths. Bowel cancer will occasionally produce tumour markers, the most common type being carcinoembryonic antigen (CEA).

Blood tests can also be used to diagnose anaemia, a symptom of bowel cancer.

How can I access bowel cancer tests?

If you're having symptoms and are worried about the possibility of bowel cancer, our bowel care diagnostic pathway is a swift and easy way to have your condition assessed. 

On the pathway, you will have an initial consultation with one of our world-class consultants, followed by a series of diagnostic bowel cancer tests based on your symptoms.

While imaging procedures can be carried out on the same day, endoscopies may happen a few days later due to the fasting period required.

If you are diagnosed with bowel cancer, your case will be taken to a multidisciplinary team (MDT) meeting for our consultants and supporting clinical staff to discuss. From there, our team will devise your personalised treatment plan.

To book your initial appointment, get in touch with our Appointments team via telephone or online through our appointment request form.

Why choose us for bowel cancer care?

At Cromwell Hospital, we hold an unwavering commitment to precision, compassion, and cutting-edge technology. Here's why you should come to us:

  • Expertise – Our renowned team of oncologists and gastrointestinal specialists brings decades of combined experience in diagnosing and treating bowel cancer. With their deep knowledge and dedication, you'll receive the best care possible.
  • State-of-the-art facilities – Our hospital in London is equipped with the latest advancements in medical technology, ensuring accurate and swift diagnoses. From advanced imaging to molecular testing, we utilize the tools that empower precise results.
  • Personalised approach – We understand that every patient's journey is unique. That's why we tailor our diagnostic approach to your individual needs, creating a comprehensive plan that maximizes accuracy and minimizes discomfort.
  • Comprehensive care – Beyond diagnosis, we offer a holistic continuum of care. Our multidisciplinary team collaborates to provide you with the best treatment options, support, and follow-up care.
  • Patient-centric experience – Your comfort and well-being are our top priorities. Our friendly staff will guide you through the process, addressing your concerns and ensuring a smooth experience.
  • Timely results – We understand the urgency of a timely diagnosis. Our streamlined processes ensure that you receive accurate results promptly, enabling swift decisions for your health.

Choose Cromwell Hospital for your bowel cancer diagnosis, and take a confident step towards a healthier future. 

Find out more about our Integrated Cancer Campus >

About the consultant

Dr Andrew Gaya is a Consultant Clinical Oncologist at Cromwell Hospital and GenesisCare, specialising in gastrointestinal tumours. He is an expert in the use of chemotherapy, radiotherapy, stereotactic radiotherapy and radiosurgery for cancer treatment, utilising state-of-the art technologies like Gamma Knife, Cyberknife and MRIdian.

Book an appointment with Dr Gaya >

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