Most screening tests find disease. Colonoscopy is unusual in that it finds and removes the precursor of disease in the same sitting, which is why it prevents cancer rather than merely detecting it.
It is also the test people most dread and most avoid, largely because of the preparation.
How Colon Cancer Develops
Most colorectal cancers begin as a polyp, a small growth on the bowel lining. Polyps are common, and the great majority never become cancerous.
Some, particularly adenomatous polyps, gradually accumulate genetic changes over roughly ten to fifteen years before becoming malignant. That long window is what makes screening so effective.
Removing a polyp during colonoscopy interrupts the sequence entirely. The cancer that would have developed simply does not. Few interventions in medicine are so directly preventive.
Who Should Be Screened
Screening recommendations depend on risk, and India lacks a national programme, so this is generally an individual decision with your doctor.
- Average risk: beginning at age forty five to fifty, repeated every ten years if normal
- Family history of colorectal cancer in a first degree relative: starting at forty, or ten years before the age at which the relative was diagnosed, whichever is earlier
- Inflammatory bowel disease: surveillance beginning eight to ten years after diagnosis
- Previous polyps: interval determined by number, size and type, commonly three to five years
- Genetic syndromes such as Lynch syndrome: starting in the twenties, repeated every one to two years
Colorectal cancer rates in India are rising, and cases in people under fifty are increasing, which is why symptoms at any age should be investigated rather than dismissed.
Symptoms That Need Investigation Regardless of Age
Screening applies to people without symptoms. If you have these, you need investigation now, not at the screening age.
- Blood in the stool, or bleeding from the rectum
- A persistent change in bowel habit lasting more than three weeks
- Unexplained weight loss
- Iron deficiency anaemia, particularly in men or postmenopausal women
- Persistent abdominal pain or a feeling of incomplete emptying
- A palpable abdominal mass
Rectal bleeding is very commonly attributed to piles, by patients and sometimes by doctors. Piles are common, and so is coexisting cancer. Bleeding deserves examination rather than assumption, particularly over forty.
The Preparation, and How to Get Through It
Bowel preparation is the part everyone dreads, and the quality of the preparation determines whether the test is worth doing. A poorly prepared colon hides polyps and often means repeating the whole thing.
- Low fibre diet for two to three days beforehand: avoid seeds, nuts, raw vegetables, whole grains and fruit skins
- Clear liquids only on the day before
- Split dosing of the laxative solution, half the evening before and half on the morning of the test, which is more effective and better tolerated
- Chill the solution and drink through a straw, which reduces the taste
- Drink clear fluids alongside to stay hydrated
- Stay near a toilet, and apply a barrier cream to prevent soreness
Discuss diabetes medication, blood thinners and iron tablets in advance, as these often need adjusting. Iron should usually be stopped a week before.
What Happens During the Test
The procedure is more comfortable than most people expect, particularly with sedation.
A flexible camera is passed through the rectum and advanced around the colon, with air or carbon dioxide used to open the bowel for viewing. The examination takes twenty to forty minutes.
Sedation is usual and most patients remember little. You will feel bloating and cramping as air is introduced, which passes. Carbon dioxide is absorbed faster than air and causes less discomfort afterwards.
Polyps found are removed during the same procedure by polypectomy, and biopsies can be taken painlessly.
Afterwards
Recovery is quick. You will rest for an hour or so while sedation wears off, and you must not drive for the rest of the day, so arrange for someone to take you home.
Bloating and passing wind are normal for a few hours. A small amount of blood after polyp removal can occur. Eat normally unless told otherwise.
Contact the hospital for severe abdominal pain, significant bleeding, fever, or vomiting. Perforation is a rare complication, occurring in a very small fraction of procedures, and is more likely when polyps have been removed.
Alternatives and Their Limits
Several other screening tests exist, and each has trade offs.
- Faecal immunochemical test: detects hidden blood in stool. Non invasive, done annually, but requires colonoscopy if positive and misses many polyps
- CT colonography: a scan producing images of the colon. Still requires bowel preparation, involves radiation, and any finding requires colonoscopy anyway
- Stool DNA tests: available in some settings, again requiring colonoscopy if positive
- Sigmoidoscopy: examines only the lower colon, missing disease higher up
The essential difference is that only colonoscopy can remove polyps. The others detect, and a positive result means you will need colonoscopy regardless.
Reducing Your Risk Otherwise
Screening is the most powerful measure. Several lifestyle factors also influence risk.
- Higher fibre intake from whole grains, pulses, vegetables and fruit
- Limiting red meat and particularly processed meat
- Regular physical activity
- Maintaining a healthy weight
- Not smoking
- Limiting alcohol
- Adequate calcium and vitamin D
None of these substitutes for screening at the appropriate age, particularly with a family history.
Colonoscopy is unpleasant to prepare for and takes half a day, and it prevents a cancer that is common and often diagnosed late. If you are over forty five, or have a family history, or have had rectal bleeding, it is worth the inconvenience.
Our gastroenterology department at T. Nagar provides colonoscopy with sedation and same day polyp removal.
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