A colonoscopy is a medical procedure used to examine the entire length of the large intestine, or colon, using a flexible tube with a camera. This procedure serves as both a diagnostic tool to investigate symptoms and a preventative screening measure against colorectal cancer. By allowing physicians to visualize the bowel lining and remove precancerous growths called polyps, a colonoscopy is highly effective in interrupting the development of cancer. Understanding the safety profile of this procedure requires a clear look at the percentage of cases that result in complications.
Overall Statistical Risk
The overall percentage of procedures resulting in a major complication is low, typically falling well below one percent. Large population studies show that the rate of serious adverse events requiring hospitalization or an emergency room visit is generally between 2.8 and 5 per 1,000 procedures, or 0.28% to 0.5%. A serious complication is defined as an event like bleeding or perforation that necessitates a hospital stay or surgical intervention. This rate can vary based on whether the procedure is purely for screening or includes therapeutic interventions.
The majority of procedures are completed without incident, highlighting the procedure’s strong safety record. In one analysis of approximately 2.8 million colonoscopies, the combined perforation rate for screening and diagnostic procedures was about 0.05% to 0.07%. While any medical procedure carries some inherent risk, the data confirms that serious harm occurs in a small fraction of cases.
Types of Complications
The most frequently reported major complications are post-polypectomy bleeding and colonic perforation. Post-polypectomy bleeding occurs when a blood vessel at the site where a polyp was removed begins to bleed. This type of bleeding is the more common of the two major risks, occurring in approximately 1.6 to 2.6 per 1,000 procedures. Bleeding can be immediate, occurring during the procedure, or delayed, presenting up to two weeks afterward.
Colonic perforation, a tear in the wall of the colon, is the most serious, though least frequent, complication. Perforation rates are estimated at around 0.5 to 1 per 1,000 procedures, or 0.05% to 0.1%. This event often requires immediate surgical repair to close the tear and prevent infection.
Other less common or minor complications include reactions to the sedation medication, such as temporary drops in blood pressure or heart rate, and post-polypectomy syndrome. Post-polypectomy syndrome involves localized burn-like injury to the colon wall that causes abdominal pain and fever. It typically resolves with observation and medication without requiring surgery.
Factors Increasing Individual Risk
While the overall complication rate is low, several factors can increase an individual’s risk profile. The largest procedural factor that modifies risk is the performance of a polypectomy, the removal of a polyp during the procedure. Colonoscopies that involve polyp removal are considered therapeutic and carry a higher risk of bleeding and perforation compared to purely diagnostic exams. The removal of large or flat polyps, which require more complex techniques, also contributes to a higher risk.
Patient-specific variables also play a role in determining individual risk. Advanced age is associated with an increased chance of complications, particularly for patients over 75 years old. The presence of existing health conditions, such as severe heart, lung, or kidney disease, can make a person more susceptible to complications related to sedation or the stress of the procedure. Patients taking blood-thinning medications have a higher risk of post-polypectomy bleeding, and these medications often require careful management and temporary cessation before the procedure.
Contextualizing Colonoscopy Risk
The low percentage of complications must be weighed against the substantial benefit of the procedure in preventing a life-threatening disease. Colorectal cancer is a common cause of cancer-related death, and colonoscopy is uniquely positioned to prevent it by detecting and removing precancerous polyps. By interrupting the cancer pathway, colonoscopy reduces the risk of developing the disease and lowers the chance of death from it.
Studies show that screening colonoscopy is associated with a reduction of colorectal cancer mortality by over 50% in certain high-risk populations. Modeling studies estimate that widespread screening can contribute to gaining 152 to 313 life-years per 1,000 people screened, demonstrating a clear benefit. The procedure transforms a potential cancer diagnosis into a simple outpatient polyp removal. For the majority of people, the preventative power of screening far outweighs the small chance of experiencing a complication.