What causes fever after a colonoscopy? A comprehensive medical guide

September 26, 2025 •

4 min read

While serious complications following a colonoscopy are rare, with rates of major adverse events remaining very low, it is important to understand the potential side effects.

So, what causes fever after a colonoscopy, and when should you seek medical advice?

This authoritative guide explains the different reasons behind a post-procedure fever and helps you differentiate between minor reactions and more serious complications.

Quick Summary

Fever after a colonoscopy is an uncommon occurrence, often indicating a mild, temporary reaction like inflammation or transient bacteremia, though rare cases may point to more significant issues such as post-polypectomy syndrome or a perforation.

Key Points

Transient Bacteremia: A low-grade fever shortly after a colonoscopy can indicate bacteria temporarily entered the bloodstream, usually resolving on its own.
Post-Polypectomy Syndrome: If polyps were removed, fever and abdominal pain can signal a localized burn to the colon wall, mimicking a perforation but less severe.
Bowel Perforation: High fever with severe, worsening abdominal pain is a medical emergency and a possible sign of a tear in the colon.
Rare Complications: Other rare causes of fever include acute cholecystitis or a reaction to anesthesia, each with its own set of distinct symptoms.
When to Call a Doctor: Contact your healthcare provider if a fever is high, persistent, or accompanied by worsening pain, heavy bleeding, or severe nausea.
Serious vs. Minor Symptoms: Learning to distinguish between mild recovery symptoms like gas and bloating versus serious signs like a rigid abdomen is critical for patient safety.

Understanding Post-Colonoscopy Side Effects

A colonoscopy is a standard medical procedure used to screen for colorectal cancer and other issues by examining the large intestine. While the procedure is generally safe, it can sometimes be followed by mild side effects like bloating, gas, and cramping. However, a fever is not considered a standard side effect and should always be evaluated, especially if it is high, persistent, or accompanied by other concerning symptoms. Understanding the potential causes can help you monitor your recovery effectively.

Potential Reasons for a Post-Colonoscopy Fever

Transient Bacteremia

One of the most common, albeit rare, reasons for a fever after a colonoscopy is a temporary presence of bacteria in the bloodstream, a condition known as transient bacteremia.

This occurs when bacteria from the colon enter the bloodstream, particularly during the removal of polyps or biopsies.
The body's immune system typically clears this without causing significant symptoms, but a mild, low-grade fever or chills can occur.
This is generally self-limiting and resolves on its own within 24-48 hours.
Routine antibiotic use is not recommended due to the low risk of serious infection.

Post-Polypectomy Syndrome

Post-polypectomy coagulation syndrome (PPCS) is a rare complication that can occur if a large polyp is removed using electrocautery.

The heat from the cautery can cause a burn that extends through the colon wall, but without creating a complete perforation.
This results in localized inflammation and can cause fever, abdominal pain, and an elevated white blood cell count.
Symptoms usually appear within 12 hours to 5-7 days after the procedure.
Diagnosis typically involves a CT scan, which would show localized wall thickening and inflammation without any extramural air, distinguishing it from a perforation.
Management is often conservative, involving intravenous fluids and close monitoring.

Bowel Perforation

Bowel perforation is one of the most serious but extremely rare complications of a colonoscopy.

This involves a tear or hole in the colon wall, allowing contents of the bowel to spill into the abdominal cavity.
Symptoms are often more severe and include intense, persistent abdominal pain that worsens over time, along with fever, nausea, and vomiting.
A CT scan or abdominal X-ray is necessary for diagnosis. A perforation is a medical emergency requiring immediate attention and often surgical repair.

Acute Cholecystitis

In very rare instances, fever and abdominal pain following a colonoscopy can be a symptom of acute cholecystitis, or inflammation of the gallbladder.

While the exact mechanism is unclear, it may be linked to procedural manipulation near the gallbladder or increased lithogenicity (stone formation).
This condition typically presents within 72 hours of the procedure and may be accompanied by abnormal liver function tests.
It is often managed with antibiotics and may require a cholecystectomy (gallbladder removal).

Reaction to Anesthesia or Medications

Some patients may experience a low-grade fever as a side effect of anesthesia or other medications used during the procedure. This is typically a benign, short-lived reaction and should resolve within a day or two. If it persists or is high, other causes should be investigated.

Dehydration

Dehydration from the bowel prep can sometimes cause a low-grade temperature. Ensuring adequate fluid intake after the procedure is important for a smooth recovery.

Normal Symptoms vs. Serious Complications

It is crucial to distinguish between normal post-procedure symptoms and those that require urgent medical attention. Here is a comparison to help you tell the difference.


Symptom	Normal Recovery	Sign of Potential Complication
Fever	Low-grade (below 100.4°F or 38°C), resolves within 1-2 days	High-grade (above 100.4°F or 38°C), persistent, or worsening
Abdominal Pain	Mild cramping or gas that improves with passing gas	Severe, worsening pain, rigid abdomen, especially if it comes on suddenly
Rectal Bleeding	Small amount of spotting that stops quickly	Heavy or continuous bleeding, passing large clots
Other Symptoms	Bloating, gas, fatigue	Nausea, vomiting, chills, shortness of breath, severe lethargy, confusion

What to Do If You Have a Fever After a Colonoscopy

Monitor Your Temperature: Use a reliable thermometer to check your temperature regularly. Note the time and reading.
Assess Other Symptoms: Pay close attention to any other signs you are experiencing, such as abdominal pain, nausea, or chills. Consider if your pain is worsening or becoming more localized.
Stay Hydrated: Ensure you are drinking plenty of fluids to help with recovery and combat potential dehydration from the bowel prep.
Inform Your Doctor: If your fever is above 100.4°F (38°C), persists for more than 24 hours, or is accompanied by other severe symptoms like worsening pain or significant bleeding, contact your doctor immediately. Do not hesitate to call your gastroenterologist's office or seek emergency care if you feel your symptoms are severe.
Avoid Self-Medicating: Do not take anti-inflammatory medications like ibuprofen unless your doctor has approved it, as they can sometimes increase the risk of bleeding after a polypectomy.

Conclusion

A fever after a colonoscopy is a symptom that warrants attention, though it is not a common side effect. Most often, a low-grade, transient fever is a benign and short-lived immune response. However, it can also be a sign of more serious, though rare, complications such as post-polypectomy syndrome or bowel perforation. By understanding the different causes and being aware of accompanying symptoms, you can better monitor your health post-procedure and know when to seek professional medical advice. Always communicate any concerns with your healthcare provider for an accurate diagnosis and treatment plan.

For more detailed information on common symptoms and potential complications, you can refer to authoritative sources such as emDocs on Post-Colonoscopy Complications.

Frequently Asked Questions

No, a fever is not a normal or common side effect of a colonoscopy. While low-grade fevers can occur in rare cases due to a benign, temporary infection, a fever should be monitored closely and reported to your doctor, as it can indicate a complication.

Post-polypectomy syndrome is a rare condition that can occur after a polyp is removed using electrocautery. It involves a transmural burn to the colon wall without perforation, leading to fever, abdominal pain, and inflammation. Symptoms usually appear within hours to days of the procedure.

You should be concerned if you develop a high fever (above 100.4°F or 38°C), or if a low-grade fever persists for more than 24 hours. You should also seek immediate medical attention if the fever is accompanied by severe or worsening abdominal pain, a rigid abdomen, or heavy rectal bleeding.

A low-grade fever can sometimes be a temporary and benign reaction to the sedative or anesthesia used during the procedure. However, because a fever can also signal more serious issues, it is important not to dismiss it without ruling out other causes, especially if it is high or doesn't resolve quickly.

Most complications, including those that cause fever, tend to occur within the first 12 hours to several days after the procedure. Some rare complications, like acute cholecystitis, can appear within 72 hours, while others, like liver abscess, may be delayed even longer.

Transient bacteremia is the temporary presence of bacteria in the bloodstream. It can happen after a colonoscopy, especially if polyps are removed, but the body usually clears it quickly. It is generally not dangerous and does not require antibiotics, but it can cause a mild, temporary fever.

Yes, dehydration from the bowel preparation before the procedure can potentially cause a low-grade fever. It is important to rehydrate properly after the colonoscopy by drinking plenty of fluids to help prevent this and aid your recovery.