Colonoscopy: reasons, benefits, risks

The colonoscopy is the most important method for the early detection of colon cancer. The gastroenterologist examines the intestine with the help of a tube-like instrument, the endoscope

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A colonoscopy can identify various diseases in the large intestine (colon) and at the end of the small intestine (terminal ileum). Gastroenterologists (gastrointestinal specialists) therefore also refer to the colonoscopy as coloileoscopy. With this method, the doctor can recognize various intestinal diseases, for example chronic and acute inflammation, circulatory disorders and protrusions of the intestine, so-called diverticula. Many patients also associate the diagnostic process with colorectal cancer screening. Colonoscopy is currently the most reliable method for detecting this type of cancer at an early stage. In addition, the doctor can remove cancer precursors (polyps) during the examination and thus drastically reduce the risk of developing colon cancer.

When is a colonoscopy considered?

Colonoscopy is used when the doctor wants to clarify certain symptoms and their underlying bowel diseases. But also for the early detection of colon cancer and its preliminary stages. If someone finds blood in the stool or if the test for invisible (occult) blood in the stool (colon cancer screening test) is abnormal, the person should urgently undergo a colonoscopy. This also applies if diarrhea, constipation or abdominal pain occur repeatedly. Other reasons for a colonoscopy: iron deficiency, anemia, unclear weight loss and increased flatulence.

Based on the symptoms and especially the colonoscopy, the doctor can determine the cause of the symptoms. For example, it can detect polyps or intestinal diverticula. The gastroenterologist can also see whether the intestinal mucosa is inflamed (for example in Crohn's disease, ulcerative colitis or after infections) or has become malignant.

The colonoscopy procedure

© W & B / Michelle Günther


© W & B / Michelle Günther

In the preliminary talk, the doctor will inform you about the advantages and disadvantages of the examination and the alternatives.

© W & B / Michelle Günther

On the day before the colonoscopy, experts recommend easy-to-digest food and avoiding coffee, tea and milk. In addition, you have to drink a laxative to cleanse your bowels - at the latest on the evening before the examination.

© W & B / Michelle Günther

Most patients are given a sedative or general anesthetic. So they don't notice anything of the reflection. Driving a car is then taboo for 24 hours.

© W & B / Michelle Günther

The doctor pushes the endoscope into the anus through the entire colon. Then he slowly pulls out the instrument. In doing so, the intestinal mucosa is considered. The procedure takes about half an hour.

© W & B / Michelle Günther

If everything is OK, you will be entitled to the examination again after ten years. Once the doctor has found and removed polyps, the time span is shortened to three or five years. In the case of cancer, further measures are taken immediately.


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You should allow two days for the preventive medical check-up. Because a colon cleanse is due beforehand, and then you should allow yourself enough rest.

How does a colonoscopy work?

In most cases, a colonoscopy is done on an outpatient basis. A few days before the colonoscopy, the attending physician explains to the patient how the examination will take place and how he should prepare.

If you want, you can get a calming and drowsy medication injected shortly before the colonoscopy. This means that almost all patients find the examination painless. It takes an average of 20 to 30 minutes.

The gastroenterologist inserts a tube-like device as thick as a finger - the endoscope - into the large intestine via the anus and lets air or carbon dioxide flow into the intestine so that it expands. Compared to air, carbon dioxide has the advantage that it is exhaled more quickly and disappears from the intestine. This will reduce the feeling of gas and gas after the exam.

The gas gives the doctor a better view of the intestinal lining. Now he pushes the endoscope, which can be controlled from the outside, up to the border between the large and the small intestine or into the end of the small intestine. Then the doctor slowly pulls the device out again. He looks at the intestinal mucosa.

The endoscope is equipped with a channel for instruments and one for rinsing or cleaning the optics. The light guide through which light is guided into the intestine is located in another channel. A small camera at the tip of the endoscope transmits the images to a monitor. With the help of this special tool, the intestinal specialist can insert instruments for tissue removal, remove polyps or carry out small surgical interventions.

When are tissue samples taken?

If the gastroenterologist discovers abnormal areas in the mucous membrane, he takes a tissue sample with the help of small forceps. He then has these examined microscopically. If the doctor wants to assess small changes in the mucous membrane more precisely, he sprays dyes on the mucous membrane or changes the light composition of the endoscope lamp. If the intestinal specialist finds smaller growths (for example polyps), they will remove them directly. These small interventions are usually not painful.

Anyone who has been given a sedative by the doctor is no longer allowed to drive a car, bicycle or motorcycle on the day of the examination. In addition, he is no longer allowed to carry out dangerous activities. Tip: Be sure to have it picked up or take a taxi home.

Are there any tips for preparation?

Patients should stop taking iron supplements three to four days before the exam. In addition, the following applies: Do not eat foods that contain grains - such as muesli, grapes, tomatoes or kiwis. The day before the colonoscopy, experts recommend easily digestible foods such as yogurt or clear vegetable broth. In addition, people must drink a laxative solution. The amount and period of intake depend on the particular preparation. Patients are normally not allowed to eat anything after noon. However, drinking is permitted and encouraged. On the day of the examination, people are not allowed to eat anything before the colonoscopy - breakfast is therefore canceled. Patients drink a second serving of the laxative in the morning to help them completely cleanse the colon. The cleaner it is, the better the gastroenterologist can assess the mucous membrane.

If you are taking blood-thinning medication, it is best to notify this immediately when making the appointment for the colonoscopy. In addition, it should be noted that the medication taken and the "pill" only have a limited or no effect at all.

What are the benefits of a colonoscopy?

Experts consider the colonoscopy to be the most accurate examination method to diagnose diseases of the intestine. The procedure enables the doctor to examine the intestinal mucosa precisely. If he finds suspicious spots, he can take a tissue sample and detect colon cancer at a very early stage. The gastroenterologist can also remove polyps during the colonoscopy. Colon cancer can develop from these benign growths. Because the doctor removes the cancer precursors during the colonoscopy, he can drastically reduce the risk of developing colon cancer.

Are there any risks?

The colonoscopy is considered a very safe procedure. Bleeding is extremely rare. A hole (perforation) caused by examination or removal of polyps is also unlikely.

In rare cases, patients cannot tolerate the sedative and develop circulatory problems. They can appear immediately after the drug is administered or during the examination. Therefore, the doctor and his team monitor the pulse, oxygen saturation and blood pressure. Immediately after the colonoscopy, the patient may still feel gas for some time. The reason: the air supplied at the beginning of the examination could not be completely extracted.

Some doctors also offer a so-called "virtual colonoscopy". The intestine is visualized on the computer using a computed tomogram or a magnetic resonance tomogram. At the moment, these procedures do not provide as meaningful results as the "real" colonoscopy. In addition, the same preparation is necessary and the doctor cannot remove discovered polyps immediately.

What else is there to consider?

If patients undergo a colonoscopy because they are taking part in colorectal cancer screening, the statutory health insurance companies cover the costs for men from the age of 50 and for women from 55 years. Men are invited to the screening earlier because they have a higher risk of colon cancer compared to women and they develop the disease earlier. If everything was in order and the patient has no symptoms, the next examination will follow ten years later.

If people have an increased risk of colon cancer, the health insurance companies will also cover the costs at an earlier age. You can clarify this individually with your health insurer or family doctor / gastroenterologist. In the case of complaints that indicate a disease in the intestinal area, the health insurance companies generally bear the costs of the colonoscopy.

Dr. Wolfgang Wegerle

© W & B / private

Consulting expert: Dr. Wolfgang Wegerle, internist and gastroenterologist

Important NOTE:
This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.

Tips for preparation: