John, 54 years old, postponed his 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 exam, the doctor found and removed, right during the colonoscopy, a polyp that already showed pre-cancerous changes. There was no surgery, no hospitalization, no cancer diagnosis. Just the exam, done at the right time.

"The data and clinical case cited in this article are fictitious and are merely illustrative, 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. But, like all invasive medical procedures, it also has real risks, which deserve to be explained clearly, without exaggeration and without minimization.

Why colonoscopy is considered so important

Colorectal cancer is among the most frequent and most deadly types of cancer in Brazil. The National Cancer Institute (INCA) estimates approximately 45,000 new cases per year in the country, and recent projections indicate a significant increase in disease mortality in the coming years, in part because diagnosis still often occurs in advanced stages.

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

What colonoscopy really diagnoses and prevents

The majority of colorectal cancers originate from polyps, benign lesions that, over time, may 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 randomized study ever conducted on the 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 exam (and did not just receive 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 alone still generates debate among researchers because of follow-up time and exam adherence in the invited group.

This scientific debate does not diminish the value of the exam. It reinforces that colonoscopy is, to this day, the most comprehensive method for finding and removing precursor lesions of colorectal cancer, and therefore remains recommended by the major medical societies in the world.

What are the risks during the exam

It is fair and important to talk about this transparently. 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 exams (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 exams (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 adverse events during the exam. Studies show that events such as oxygen desaturation, blood pressure changes, and arrhythmias occur in up to 0.9% of sedated procedures, accounting for approximately 67% of all unplanned adverse events recorded during or after colonoscopy.
  • Splenic injury and post-polypectomy syndrome: are rare complications, occurring in a few cases per 100,000 exams.

Factors that increase this risk include advanced age, prior cardiovascular or pulmonary disease, and exam performance by a professional with low procedural volume, which reinforces the importance of undergoing colonoscopy with an experienced endoscopist in a facility with proper monitoring structure.

What about deaths related to colonoscopy? What science shows, and why they happen

This is the point that generates the most fear, so it is worth explaining carefully. The numbers published in the literature vary widely, from approximately 1 death per 10,000 exams 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 exam, even when the cause of death has no relation whatsoever to the colonoscopy. An illustrative example comes from an Australian study with more than 23,000 patients: there were 196 deaths within 30 days after the exam, but only 3 of those deaths (1.2 per 10,000 exams) were actually attributed to colonoscopy. The others were related 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 exams found a rate of approximately 0.007%, equivalent to approximately 1 in 14,000 procedures. A study from the national screening program in the Netherlands, with more than 172,000 colonoscopies, arrived at a similar number: approximately 1 death per 11,000 exams related to the procedure.

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

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

Putting the numbers in perspective

For most people with clinical indication for colonoscopy, whether by 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 exam should consider age, health history, and individual risk factors, and this assessment is precisely the doctor's role before recommending the procedure.

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

Dr. Rebeca Soares Andrade CRM - GO 39335