Risks & Safety
Understanding colonoscopy safety and rare complications
Colonoscopy is very safe
Colonoscopy is one of the most commonly performed and safest procedures in gastroenterology. Millions are performed every year in Canada and worldwide. Serious complications are rare, occurring in less than 1 in 1,000 screening colonoscopies. Your gastroenterologist will discuss the specific risks with you before the procedure.
📊Complication Rates in Perspective
99.9%
of screening colonoscopies have no serious complications
<0.1%
risk of perforation (a hole in the colon wall)
0.1-0.6%
risk of significant bleeding after polyp removal
To put this in perspective: the lifetime risk of developing colorectal cancer without screening is approximately 4-5%. The small risks of colonoscopy are far outweighed by the cancer prevention benefit.
📋Understanding Specific Risks
Bleeding
Minor bleeding can occur after polyp removal and usually stops on its own. Significant bleeding requiring intervention occurs in about 0.1-0.6% of cases where polyps are removed. Risk is higher with larger polyps or if you take blood-thinning medications. A small amount of blood in your first bowel movement after the procedure is normal.
Perforation
A perforation (small tear or hole in the colon wall) is the most serious but rarest complication, occurring in less than 1 in 1,000 screening colonoscopies. Risk is slightly higher when polyps are removed. If it occurs, it can usually be treated with antibiotics and bowel rest, but may rarely require surgery. This is why it's important to report severe abdominal pain after the procedure.
Post-Polypectomy Syndrome
After removal of a large polyp, you may develop localized abdominal pain, low-grade fever, and an elevated white blood cell count. This happens when there is thermal injury to the colon wall without a full-thickness tear. It typically resolves with antibiotics and rest — no surgery needed.
Sedation-Related Risks
Sedation medications can very rarely cause breathing problems, changes in heart rate, or allergic reactions. Your vital signs are continuously monitored throughout the procedure by a dedicated team member. Patients with sleep apnea, severe lung or heart disease, or obesity may have slightly higher sedation risk — let your doctor know about these conditions.
Infection
The risk of infection from a colonoscopy is extremely low. Colonoscopes undergo rigorous high-level disinfection or sterilization between procedures, following strict national and provincial protocols. Report any fever above 38.5°C (101°F) after the procedure to your doctor.
Incomplete Examination
Occasionally, the colonoscope cannot reach the beginning of the colon (cecum) due to anatomical factors, adhesions from prior surgery, or inadequate bowel preparation. If this happens, your doctor may recommend a repeat procedure or an alternative test like CT colonography. This is not a complication per se, but it means the screening may need to be completed another way.
💧Bowel Preparation Risks
The bowel preparation itself carries small risks that are important to understand:
- •Dehydration — The prep causes significant fluid loss. Drink plenty of clear fluids throughout. Signs of dehydration include dizziness, dry mouth, and dark urine.
- •Electrolyte imbalance — Drink a variety of fluids (not just water) to replace electrolytes. Sports drinks, clear broth, and clear juices help maintain balance.
- •Nausea/vomiting — Some patients feel nauseated during prep. Drinking slowly, chilling the solution, and taking breaks between glasses can help. If persistent vomiting prevents you from completing the prep, call your doctor.
- •Kidney concerns — Certain prep solutions (particularly sodium phosphate-based) are not recommended for patients with kidney disease. Your doctor chooses the safest prep for your health profile.
🚨When to Seek Medical Attention After Your Procedure
Contact your doctor or go to the emergency department if you experience any of the following after your colonoscopy:
Severe or worsening abdominal pain (not just mild bloating)
Heavy rectal bleeding (more than a tablespoon of bright red blood)
Persistent bleeding that doesn't stop
Fever above 38.5°C (101°F)
Severe nausea or vomiting
Inability to pass gas or have a bowel movement for more than 24 hours after procedure
Chest pain, difficulty breathing, or fainting
Abdominal swelling or firmness
In BC: If you need urgent advice, call 811 (HealthLink BC) to speak with a registered nurse 24/7. For emergencies, call 911 or go to your nearest emergency department.
✅How We Keep You Safe
Board-certified gastroenterologists with specialized training and ongoing quality monitoring
Continuous vital sign monitoring — oxygen, heart rate, blood pressure throughout the procedure
National safety standards for colonoscope reprocessing and disinfection
Quality metrics tracked — including cecal intubation rate, adenoma detection rate, and complication rates
Pre-procedure assessment — your health history, medications, and risk factors are reviewed before the procedure to ensure safety