What Is a Colonoscopy?

A colonoscopy is a procedure used to examine the inner surface of the large intestine for cancer, polyps, and other structural abnormalities. The colonoscope is a long, thin, flexible instrument equipped with a high-resolution camera at its tip, allowing detailed visualization of the entire colon. The procedure is usually performed on an outpatient basis and causes minimal discomfort. In addition to diagnostic purposes, therapeutic interventions such as polyp removal can be performed simultaneously.

Who Should Undergo a Colonoscopy?

Colonoscopy is performed for diagnostic purposes in individuals who exhibit certain signs of colon cancer and for screening purposes in individuals at risk of developing the disease, even if no symptoms are present.

Diagnostic Colonoscopy

Colon cancer is often a silent disease that may not cause symptoms for a long time.
Possible indications for diagnostic colonoscopy include:

  • Blood in the stool

  • Anemia (low red blood cell count)

  • Changes in bowel habits

  • Thinning of the stool

  • Abdominal discomfort (gas, bloating, fullness, cramps, etc.)

  • Vomiting

  • Diarrhea, constipation, or a sensation of incomplete evacuation

  • Frequent gas pain

  • Unexplained weight loss

  • Rectal bleeding

  • Persistent fatigue or weakness during routine activities

If any of these symptoms persist for more than two weeks, consult your doctor. If bleeding is present, immediate evaluation is necessary. In individuals over the age of 40 with iron deficiency, colonoscopy is recommended. Although these symptoms are not specific to colon cancer, if they persist longer than two weeks, a colonoscopy should be considered.

Screening Colonoscopy

Colon cancer symptoms often appear in advanced stages, and in some cases, even after metastasis. Therefore, colonoscopy screening is recommended for individuals at risk, even if no obvious symptoms are present. The goal is to detect the disease at the earliest possible stage to ensure successful treatment.

Those with a family history of colon or rectal cancer are at a higher risk and should be evaluated for screening colonoscopy.

The risk of developing colon cancer increases with age. Men and women over 50 have an equal risk of developing the disease. For this reason, colorectal cancer screening is recommended for individuals aged 45 and older.
People with a personal or family history of colorectal cancer or polyps are at greater risk.
Screening before the age of 45 is recommended for high-risk individuals, including those with:

  • Personal or family history of inflammatory bowel disease (Ulcerative Colitis, Crohn’s Disease)

  • Colorectal cancer or polyps

  • History of ovarian, endometrial (uterine), or breast cancer

For individuals with a close relative diagnosed with colorectal cancer or polyps, the first screening colonoscopy should be performed at age 40 or 10 years earlier than the age at which the relative was diagnosed. If results are normal, colonoscopy should be repeated every 5 years.

Other Indications for Colonoscopy

  • Follow-up in individuals who have undergone surgery or treatment for colon or rectal cancer

  • Monitoring of patients diagnosed with inflammatory bowel disease (Ulcerative Colitis or Crohn’s Disease)

Which Physicians Perform Colonoscopy?

Colonoscopy is performed by general surgeons, gastrointestinal surgeons, and gastroenterologists.

How Is a Colonoscopy Performed?

Bowel cleansing is required 1–2 days before the procedure. A detailed instruction form is provided to patients at the time of scheduling, explaining dietary restrictions, timing and dosage of prescribed laxatives or liquids, and enema procedures.
Adequate preparation is confirmed when bowel movements become clear and watery.
If the colon is not properly cleansed and residual stool remains, visualization may be impaired, requiring the procedure to be repeated. Therefore, proper preparation is essential.

During the procedure, sedatives are administered intravenously to ensure comfort and minimize pain.
The colonoscope is inserted through the anus and advanced through the rectum to visualize all sections of the colon up to where it connects with the small intestine.
Polyps identified during the procedure are removed, and biopsies are taken from suspicious or abnormal areas for pathological examination.

The procedure typically lasts less than one hour. Some patients may experience mild bloating afterward, which usually resolves after passing gas. Due to sedative effects, most patients do not recall the procedure.
A companion should accompany the patient before and after the procedure.
If no complications arise, patients can eat within a few hours. Driving is not recommended on the same day, and rest at home is advised.

Are There Any Complications of Colonoscopy?

Colonoscopy is a safe procedure, and complications occur in less than 1% of patients. Rare risks include bleeding, perforation (bowel wall injury), and side effects from sedative medications.
In approximately 10–12% of cases, the entire colon may not be visualized due to anatomical factors, and the procedure may be stopped if continuing is deemed risky by the physician. In such cases, the examination can be repeated on another day or supplemented with additional imaging methods such as CT colonography.