Risks & Safety
Understanding colonoscopy safety and rare complications
Colonoscopy is very safe
A colonoscopy is one of the safest procedures in medicine. Millions are done safely every year. Serious problems are rare — less than 1 in 1,000 screening colonoscopies. Your doctor will go over the 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: without screening, about 4 to 5 out of 100 people will get colon cancer in their lifetime. The small risks of a colonoscopy are far outweighed by the cancer prevention benefit.
📋Understanding Specific Risks
Bleeding
Minor bleeding can happen after polyp removal. It usually stops on its own. Heavier bleeding that needs treatment happens in less than 1 in 200 cases. The risk is higher with larger polyps or if you take blood thinners. A small amount of blood in your first bowel movement after the procedure is normal.
Perforation
A perforation is a small tear or hole in the colon wall. This is the most serious but rarest problem — less than 1 in 1,000 screening colonoscopies. It is slightly more likely when polyps are removed. If it happens, it can usually be treated with antibiotics and rest. Surgery is rarely needed. This is why you should report bad belly pain after the procedure.
Post-Polypectomy Syndrome
After a large polyp is removed, you may get belly pain and a low fever. This happens when the colon wall gets irritated but is not torn. It usually gets better with antibiotics and rest. Surgery is not needed.
Sedation-Related Risks
Sleep medicine (sedation) can very rarely cause breathing problems, heart rate changes, or allergic reactions. Your vital signs are watched the whole time by a team member. If you have sleep apnea, lung or heart disease, or obesity, let your doctor know — they may need to take extra care.
Infection
The chance of getting an infection from a colonoscopy is extremely low. The camera tubes are cleaned and disinfected carefully between each use, following strict national rules. Tell your doctor if you get a fever above 38.5°C (101°F) after the procedure.
Incomplete Examination
Sometimes the camera cannot reach the end of the colon. This can happen because of body shape, scar tissue from past surgery, or poor prep. If this happens, your doctor may suggest doing it again or using a different test (like a CT scan). This is not a complication, but it means the screening may need to be finished another way.
💧Bowel Preparation Risks
The bowel preparation itself carries small risks that are important to understand:
- •Dehydration — The prep causes you to lose a lot of fluid. Drink plenty of clear fluids. Watch for signs of dehydration: dizziness, dry mouth, and dark urine.
- •Electrolyte imbalance — Drink different types of fluids, not just water. Sports drinks, clear broth, and apple juice help keep your body in balance.
- •Nausea — Some people feel sick during prep. Try drinking slowly, chilling the solution, and taking breaks between glasses. If you cannot stop vomiting, call your doctor.
- •Kidney concerns — Some prep solutions are not safe for people with kidney disease. Your doctor will choose the safest prep for you.
🚨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
Trained specialists — your procedure is done by a doctor with years of specialized training
Constant monitoring — your oxygen, heart rate, and blood pressure are watched the whole time
Strict cleaning rules — the equipment is thoroughly cleaned and disinfected after every use
Quality tracking — hospitals track success rates and complication rates to keep improving
Health check before the procedure — your health history and medications are reviewed to make sure everything is safe