Colonoscopy

The large bowel is the last part of the digestive tract, about one and a half metres long, where water is absorbed and stool is formed. Colonoscopy examines its entire length, from the rectum up to the junction with the small intestine, using a colonoscope: a flexible tube about the width of a finger with a light, a high-definition camera and a channel for small instruments. Air or carbon dioxide gently opens the bowel so the lining can be seen on a screen. Through the channel the specialist can take biopsies, remove polyps, mark a spot with ink for a surgeon, stop minor bleeding or widen a narrowing. This combination is what distinguishes colonoscopy from scans and stool tests: it does not only show a problem, it can confirm it under the microscope and often treat it at once. Removing precancerous polyps before they change is the main way colonoscopy helps prevent bowel cancer.

Doctors recommend colonoscopy in three broad situations. The first is screening: people of average risk are usually offered bowel cancer screening from around the age of 45 to 50, and those with a strong family history, certain inherited syndromes or a positive stool test are advised to have colonoscopy earlier or more often. The second is investigation of symptoms, such as blood in the stool, a lasting change in bowel habit, unexplained weight loss, iron-deficiency anaemia, persistent abdominal pain or chronic diarrhoea. The third is surveillance: after polyps or bowel cancer have been removed, and in long-standing ulcerative colitis or Crohn's disease affecting the colon, repeat examinations are scheduled at set intervals. Colonoscopy is also used to clarify abnormal findings on a CT scan. When the question concerns the stomach or upper intestine instead, an upper GI endoscopy is the matching test, and the two are often done in one session.

You change into a gown and a small cannula is placed in a vein in your arm. Most units give conscious sedation with a painkiller, or a short-acting anaesthetic medicine given by an anaesthesia team, so you are drowsy or asleep and comfortable; some people choose to have it with little or no sedation. You lie on your left side, and the specialist passes the colonoscope through the anus and steers it around the bends of the colon to its start, the caecum. The detailed inspection happens mostly on the way back out, slowly and carefully. Polyps are removed with a small wire loop or forceps, and samples go to the laboratory. Gentle pressure on the abdomen or a change of position sometimes helps the scope round a bend. The examination usually takes about 20 to 45 minutes. Afterwards you rest in a recovery area until the sedation wears off, and the findings are explained to you before you leave.

Almost any adult who needs the bowel examined can have a colonoscopy, though the team reviews heart and lung conditions, kidney function and pregnancy before choosing the preparation and sedation. The key to a good examination is a clean bowel. For a few days you may be asked to avoid seeds, nuts and high-fibre foods, and the day before you switch to clear fluids and drink a prescribed laxative solution, often split between the evening before and the morning of the test. Blood thinners, iron tablets and diabetes medicines need specific advice, so bring a full medicine list. Because sedation affects judgement, you will need a companion to take you back to your accommodation, and you should not drive or sign important documents for the rest of the day. International patients can usually start remotely: the team reviews symptoms, earlier reports and medicines, and sends preparation instructions before you travel.

Recovery is usually quick. Bloating and mild cramping from the gas used during the test pass within a few hours, and you can normally eat once you are awake, starting with something light. Most people feel back to normal the next day. A small amount of blood in the first stool after polyp removal can be expected, but heavy bleeding, worsening abdominal pain or fever needs prompt medical attention, and bleeding after polyp removal can occasionally appear several days later. For this reason, when a large polyp has been removed, the team may ask you to stay a little longer before a long flight. Many visitors plan two to three days in total: one for the consultation and preparation, one for the test and a buffer day. Laboratory results take longer, so agree in advance how they will be shared, typically through a written report and a remote consultation with the specialist.

Colonoscopy is a routine and generally safe examination, but it is an invasive test with uncommon risks. Sedation can lower blood pressure or slow breathing, which the team monitors throughout. Bleeding can follow polyp removal; it usually stops by itself or is treated through the scope. A perforation, a small tear in the bowel wall, is rare and is more likely when large polyps are removed; it may need repair, sometimes by surgery. A colonoscopy can miss a small polyp, particularly if the bowel preparation was poor, which is why a clean bowel and a careful, unhurried withdrawal matter. The report states how complete the examination was and the quality of the preparation. Results also set your next step: a clear examination often means no repeat for several years, whereas polyps or inflammation lead to a tailored surveillance interval or further treatment.