Colonoscopy

A colonoscopy is a procedure in which a doctor uses a thin, flexible tube with a camera on its tip to look directly inside your large intestine (colon) and rectum.

The tube, called a colonoscope, is gently guided through the entire length of the colon. The live camera feed lets the doctor spot abnormal growths, inflamed tissue, bleeding sources, or other changes along the inner wall of the bowel. If something suspicious is found, the doctor can pass small tools through the same tube to take a tissue sample (biopsy) or remove a polyp (a small abnormal growth) on the spot — so the procedure can be both diagnostic and therapeutic in a single session.

Colonoscopy is used both to investigate symptoms and to screen for disease in people who have no symptoms at all. Doctors in the field of gastroenterology (the specialty covering the digestive system) recommend it for a wide range of situations.

• Rectal bleeding or blood mixed into the stool
• Persistent changes in bowel habits — such as ongoing diarrhoea or constipation that has no clear cause
• Unexplained abdominal pain or cramping
• Unexplained weight loss or anaemia (low red blood cell count) that may point to a bowel source
• Routine screening for colorectal cancer (cancer of the colon or rectum) in adults at average or higher-than-average risk
• Surveillance after previous polyps or colorectal cancer have been treated
• Monitoring of inflammatory bowel disease (IBD) — conditions such as Crohn's disease or ulcerative colitis, which cause long-term inflammation of the gut
• Confirming or ruling out findings seen on other imaging tests such as CT or MRI
• Removing polyps before they can develop into cancer
• Treating a source of bleeding inside the colon using specialised tools passed through the colonoscope

Colonoscopy is not always the right choice. Your doctor will consider alternatives or extra precautions if any of the following apply.

• A suspected or confirmed perforation (hole) in the bowel wall — this is usually a medical emergency requiring different treatment
• Severe, active inflammation of the colon that makes the bowel wall fragile
• Very recent heart attack or serious heart rhythm problems that make sedation (medicine to make you drowsy and relaxed) too risky
• Inability to complete the bowel preparation needed to clear the colon — for example, in some patients with severe kidney disease
• Pregnancy, where the timing and necessity of the procedure will be carefully weighed by the medical team

Colonoscopy is generally considered a safe procedure, but like any medical intervention it carries some recognised risks, which your doctor will discuss with you beforehand.

• Bloating, wind, and mild abdominal cramping after the procedure — the most common experience, usually settling within a few hours
• Reactions to sedation, such as nausea, dizziness, or a temporary drop in blood pressure
• Bleeding at the site where a polyp was removed or a biopsy was taken — usually minor and self-limiting, but occasionally requires further treatment
• Perforation (a small tear in the bowel wall) — a rare but serious complication that may require surgical repair
• Missed lesions — very small polyps or flat growths can occasionally be overlooked, especially if bowel preparation was incomplete
• Infection — uncommon, but the risk is slightly higher if therapeutic steps such as polyp removal were performed
• Aspiration (inhaling stomach contents into the lungs) — a rare risk associated with sedation, more likely if fasting instructions were not followed

Good preparation is essential for a colonoscopy. If the colon is not completely clear, the doctor may miss important findings or the procedure may need to be repeated. Your care team will give you detailed written instructions tailored to your situation, but the following gives a general picture of what to expect.

In the days before the procedure, you will usually be asked to follow a low-fibre or clear-liquid diet to reduce the amount of waste in the bowel. You will be prescribed a bowel-cleansing solution (laxative) to take at home — often split into a dose the evening before and a dose on the morning of the procedure. This causes several hours of loose stools, which is expected and necessary. Most hospitals ask you to fast (no food or drink) for a set number of hours before the sedation is given; your team will specify the exact cut-off time. Alcohol should be avoided for at least a day or two beforehand. Smoking is best avoided on the day, as it can affect sedation.

Regarding medications, tell your doctor about everything you take regularly, including herbal supplements. Blood thinners (medicines that reduce clotting) are commonly paused for several days before the procedure if polyp removal is anticipated. Iron supplements are usually stopped about a week ahead because they darken stool and coat the bowel wall, making it harder to see. Diabetes medications may need timing adjustments around the fasting period. Your doctor will decide which medicines to continue unchanged.

Before the colonoscopy, your doctor will typically review your medical history and check relevant results. Common pre-procedure assessments may include:

• Blood tests to check clotting ability and general health markers
• An electrocardiogram (EKG — a tracing of the heart's electrical activity) if you have heart disease or are older
• Review of any recent CT, MRI, or ultrasound (USG) images of the abdomen

On the day of the procedure, the steps typically unfold as follows:

• You arrive at the endoscopy unit and change into a hospital gown.
• A nurse checks your blood pressure, heart rate, and oxygen levels, and places a small intravenous (IV) line — a thin tube in a vein, usually in your arm — for giving fluids and sedation.
• The doctor or anaesthetist explains what will happen and asks you to sign a consent form confirming you understand the procedure and its risks.
• Sedation is given through the IV line. Most patients receive a light-to-moderate sedative that makes them drowsy and comfortable but not fully unconscious; some centres offer deeper sedation. Your oxygen level and heart rate are monitored throughout.
• You are positioned lying on your side, usually with knees drawn up.
• The doctor gently inserts the colonoscope through the rectum and advances it slowly around the entire colon, using air or carbon dioxide to gently inflate the bowel so the walls can be seen clearly.
• The doctor carefully examines the lining of the bowel as the scope is slowly withdrawn. This withdrawal phase is when most findings are identified.
• If a polyp is found, it is usually removed at the same time using a wire loop or other tool passed through the colonoscope. If tissue sampling is needed, a small biopsy forceps (tiny grabbing tool) is used.
• The colonoscope is fully removed, and you are moved to a recovery area to wake up from the sedation.

After the colonoscopy, you will be observed in a recovery area until the sedation has worn off sufficiently — this usually takes between thirty minutes and a couple of hours, though individual responses vary. You will not be allowed to drive yourself home on the day of the procedure, so arrange for a responsible adult to accompany you. Your care team will give you written discharge instructions before you leave.

• Expect bloating and wind for several hours after the procedure; walking around gently can help the gas pass.
• If sedation was used, avoid driving, operating machinery, signing legal documents, or making important decisions for the rest of that day.
• Eating and drinking can usually resume with light foods once you feel ready and the care team confirms it is safe.
• If a polyp was removed, your doctor will usually recommend avoiding blood thinners for a period they specify, to reduce the risk of delayed bleeding.
• Watch for warning signs and seek medical attention promptly if you notice heavy rectal bleeding, severe abdominal pain, a hard or very tender abdomen, fever, or feeling faint — these can indicate a complication.
• Biopsy results are not immediate; tissue samples are sent to a pathology laboratory and results typically take several days to about two weeks, depending on the facility.
• A follow-up appointment will be scheduled to discuss results, further treatment if needed, and when the next colonoscopy — if any — should be performed.
• If inflammatory bowel disease or another chronic condition is being monitored, your gastroenterologist will outline a longer-term surveillance schedule.
• For polyp removal or cancer screening purposes, the recommended interval before the next colonoscopy depends on what was found and will be explained by your doctor.