John, 54 years old, postponed colonoscopy for nearly four years. He had no symptoms, just embarrassment about the preparation and some fear of the procedure. When he finally had the examination, the doctor found and removed, during the colonoscopy itself, a polyp that already showed pre-cancerous changes. There was no surgery, no hospitalisation, no cancer diagnosis. Just the examination, done at the right time.

"The data and clinical case cited in this article are fictitious and are merely illustrative in purpose, serving to facilitate understanding of the topic addressed."

This is the logic behind colonoscopy: it is not just for diagnosing colorectal cancer, it is for preventing it from forming. However, like any invasive medical procedure, it also carries real risks, which deserve to be explained clearly, without exaggeration and without minimisation.

Why colonoscopy is considered so important

Colorectal cancer is among the most frequent and most lethal types of cancer in Brazil. The National Cancer Institute (INCA) estimates about 45,000 new cases per year in the country, and recent projections indicate significant increases in mortality from the disease in the coming years, partly because diagnosis still usually occurs at advanced stages.

This happens because colorectal cancer is often silent in its early stages. Bleeding, changes in bowel habits and weight loss usually appear when the disease is already more advanced. Colonoscopy changes this scenario because it allows visualisation of the entire colon and identification of lesions long before they cause any symptoms.

What colonoscopy really diagnoses and prevents

Most colorectal cancers begin from polyps, benign lesions that, over time, can undergo transformations and progress to cancer. During colonoscopy, these polyps can be removed at the same moment they are found, which interrupts this process before it advances.

The largest randomised study ever conducted on this topic, the NordICC, followed more than 84,000 people in Poland, Norway and Sweden for ten years. Among those invited to undergo screening colonoscopy, the incidence of colorectal cancer fell 18% compared to those not invited. Among people who actually underwent the examination (and not just received the invitation), the reduction in incidence reached 31%, and the reduction in deaths from the disease reached 50%. A more recent update of the same study, with 13 years of follow-up, confirmed the reduction of approximately 20% in incidence, although the impact on mortality specific to colorectal cancer, in isolation, still generates debate among researchers because of the follow-up time and adherence to the examination in the invited group.

This scientific debate does not diminish the value of the examination. It reinforces that colonoscopy is, to this day, the most comprehensive method for finding and removing lesions that precede colorectal cancer, and for this reason remains recommended by the major medical societies worldwide.

What are the risks during the examination

It is fair and important to speak about this with transparency. No invasive procedure is free from risk, and colonoscopy is no exception. The most studied complications are:

  • Intestinal perforation: occurs in approximately 5 per 10,000 examinations (0.05%), according to a global meta-analysis published in 2025 in the American Journal of Gastroenterology. The risk increases when polyp removal (polypectomy) is associated.
  • Bleeding: occurs in approximately 18 per 10,000 examinations (0.18%) in the general population, and is more frequent when larger polyps are removed during the procedure.
  • Cardiopulmonary complications related to sedation: are, in practice, the most common cause of complications during the examination. Studies show that events such as drop in oxygenation, changes in blood pressure and arrhythmias occur in up to 0.9% of sedated procedures, accounting for approximately 67% of all unplanned complications recorded during or after colonoscopy.
  • Splenic injury and post-polypectomy syndrome: are rare complications, occurring in just a few cases per 100,000 examinations.

Factors that increase this risk include advanced age, prior cardiovascular or pulmonary disease, and performance of the examination by a professional with low procedure volume, which reinforces the importance of undergoing colonoscopy with an experienced endoscopist, in a service with adequate monitoring infrastructure.

And deaths related to colonoscopy? What does science show, and why do they occur

This is the point that generates the most fear, so it is worth explaining carefully. The numbers published in the literature vary considerably, from approximately 1 death per 10,000 examinations to 1 per 50,000, and this variation has an important methodological explanation.

Many studies count any death occurring up to 30 days after the examination, even when the cause of death has no relation whatsoever to the colonoscopy. A very illustrative example comes from an Australian study with more than 23,000 patients: there were 196 deaths within 30 days after the examination, but only 3 of these deaths (1.2 per 10,000 examinations) were, in fact, attributed to colonoscopy. The others were linked to other causes, which is expected in a population that often already has other health conditions.

When looking specifically at deaths caused by colonoscopy, a review of more than 370,000 examinations found a rate of approximately 0.007%, equivalent to approximately 1 in every 14,000 procedures. A study from the Netherlands' national screening programme, with more than 172,000 colonoscopies, arrived at a similar number: approximately 1 death per 11,000 examinations related to the procedure.

And why do these deaths occur? The same Dutch research details the proportion: approximately 50% of deaths related to colonoscopy were associated with cardiovascular events, usually linked to sedation or the need to temporarily suspend anticoagulant medications before the examination. The other half focuses mainly on complications from intestinal perforation, such as infection and peritonitis, when this injury is not identified and treated in time.

In summary, deaths attributable to colonoscopy are rare, and when they do occur, they are concentrated in two main mechanisms: cardiovascular response to sedation and infectious complications from perforation. This explains why careful screening of comorbidities before the examination, and continuous monitoring during the procedure, are central safety steps, not merely formality.

Putting the numbers in perspective

For most people with a clinical indication for colonoscopy, whether due to age, family history or symptoms, the risk of serious complications is low, and the risk of death is extremely low when compared to the benefit of finding and removing a lesion before it becomes cancer. Science is clear on one point: the decision to undergo the examination should consider age, health history and individual risk factors, and this assessment is precisely the role of the doctor in indicating the procedure.

This content is for informational and educational purposes and does not replace medical consultation, diagnosis or treatment. Each case should be individually evaluated by a healthcare professional, considering clinical history, complementary examinations and personal risk factors.

Dr. Rebeca Soares Andrade CRM - GO 39335