What Is A Proctosigmoidoscopy Procedure Explained?

A proctosigmoidoscopy is an exam that lets a doctor look directly at the lower part of your colon and your rectum. A thin, flexible tube with a light and camera is inserted through the anus to check the last section of the large intestine, called the sigmoid colon, along with the rectum. It is one of several tests used to screen for colorectal cancer and to investigate symptoms like bleeding or persistent changes in bowel habits.

What Is a Proctosigmoidoscopy Procedure Explained

A proctosigmoidoscopy examines the rectum and the sigmoid colon — the S-shaped section of the large intestine closest to the rectum. The instrument used is called a sigmoidoscope. It is a flexible tube roughly the thickness of a finger, with a light and a small camera at the tip.

The doctor inserts the tube through the anus and gently guides it into the colon. The camera sends images to a monitor, letting the doctor see the lining of the bowel in real time. The exam typically reaches about the lower third of the colon. It does not examine the upper sections — the descending colon, transverse colon, or ascending colon.

This distinction matters. A proctosigmoidoscopy is not the same as a colonoscopy. A colonoscopy examines the entire colon, while a proctosigmoidoscopy looks only at the rectum and sigmoid colon. That difference affects what the test can find and how often it needs to be repeated.

The procedure usually takes about 5 to 10 minutes. It can be done in a doctor’s office or an outpatient clinic. Most people do not need sedation, though some clinics offer it.

Why Would a Doctor Recommend This Procedure?

There are two main reasons: screening for colorectal cancer and investigating symptoms.

For screening, a proctosigmoidoscopy can find polyps and early cancers in the lower colon. Polyps are growths on the bowel lining. Some polyps can eventually become cancer if they are not removed. During the exam, the doctor can remove small polyps or take tissue samples called biopsies.

For symptoms, a doctor might recommend this test if you have:

• Rectal bleeding or blood in your stool
• A lasting change in bowel habits, such as diarrhea or constipation that does not go away
• Unexplained abdominal pain
• A feeling that you still need to go after a bowel movement

These symptoms have many possible causes, and most are not cancer. But direct examination of the lower bowel helps doctors rule out serious problems or find them early.

How Is It Different From a Colonoscopy?

The key difference is how much of the colon each test can see. A colonoscopy examines the entire colon. A proctosigmoidoscopy examines only the rectum and sigmoid colon — roughly the lower third.

This has real consequences. A proctosigmoidoscopy cannot detect polyps or cancers in the upper colon. Research has shown that a significant portion of colorectal cancers occur in areas this test cannot reach. That is one reason colonoscopy is more commonly used for screening in the United States.

Another difference is preparation. A colonoscopy requires cleaning out the entire colon with a liquid diet and strong laxatives the day before. A proctosigmoidoscopy needs only an enema or a small amount of liquid preparation to clear the lower bowel. That makes it faster and easier for the patient.

Sedation is another difference. Colonoscopy usually involves sedation. Proctosigmoidoscopy typically does not.

What Happens During the Procedure?

You will lie on your left side with your knees pulled toward your chest. The doctor gently inserts the sigmoidoscope into your rectum and advances it into the sigmoid colon. Air may be pumped in to open the bowel so the camera can see clearly.

You may feel pressure, mild cramping, or the urge to have a bowel movement. These sensations are common and usually pass quickly. The exam itself is short — typically under 10 minutes.

If the doctor sees a small polyp, it can often be removed during the same exam. Larger polyps or suspicious areas may be biopsied instead. Biopsy means taking a tiny tissue sample to send to a lab for testing.

After the procedure, you can usually go back to your normal activities right away. Some people feel bloated or pass gas for a short time because of the air used during the exam.

What Are the Risks?

Proctosigmoidoscopy is generally considered a low-risk procedure. But no medical test is completely without risk.

The most common after-effects are mild bloating, gas, and slight cramping. These usually resolve within hours.

Serious complications are rare. They include:

• Bleeding, especially if a polyp was removed or a biopsy was taken
• Perforation — a tear in the bowel wall
• Infection
• Reaction to sedation, if sedation was used

Perforation is uncommon. When it does happen, it requires immediate medical attention and may need surgery. The risk is higher when polyps are removed or when the procedure is done in someone with active inflammation or a known narrowing of the bowel.

Call your doctor right away if you have severe pain, heavy bleeding, fever, or a hard, swollen abdomen after the procedure.

How Do You Prepare for It?

Preparation is simpler than for a colonoscopy. Your doctor will give you specific instructions, but in general:

• You may be asked to use an enema or a small liquid preparation to clear the lower bowel
• You may need to avoid solid food for a few hours before the exam
• You may need to stop certain medications, such as blood thinners, for a short time

Tell your doctor about all medications you take, including over-the-counter drugs and supplements. Blood thinners can increase the risk of bleeding, especially if a polyp is removed.

If you have a condition like diabetes, ask your doctor how to manage your medications around the procedure.

What Do the Results Mean?

If the exam is normal, no polyps or abnormal tissue were found in the area examined. Your doctor will recommend when to repeat the test or whether another type of screening is needed.

If a polyp was found and removed, the lab will examine it. Most polyps are benign, but some have the potential to become cancer over time. The type of polyp and its size affect what comes next.

If a biopsy was taken, results usually come back within a few days to a week. Your doctor will explain what was found and whether further testing or treatment is needed.

One important point: a normal proctosigmoidoscopy does not rule out problems in the upper colon. If your doctor suspects an issue beyond the reach of this test, a colonoscopy may be recommended.

Is It Still Used for Screening?

Proctosigmoidoscopy was once a common screening tool for colorectal cancer. Its use has declined in the United States as colonoscopy became more widespread. Colonoscopy examines the whole colon and allows removal of polyps throughout, which is why many guidelines now favor it.

That said, proctosigmoidoscopy is still used in some situations. It may be appropriate for people who cannot or will not undergo a full colonoscopy. It is also used to evaluate symptoms limited to the lower bowel.

Some research suggests that flexible sigmoidoscopy screening can reduce deaths from colorectal cancer, particularly cancers in the lower colon. But it does not protect against cancers in the upper colon, which a colonoscopy can detect.

The choice between tests depends on your personal risk, your preferences, and your doctor’s judgment. There is no single right answer for everyone.

When Should You Talk to Your Doctor?

Talk to your doctor if you have rectal bleeding, a lasting change in bowel habits, unexplained weight loss, or abdominal pain that does not go away. These symptoms do not automatically mean cancer, but they deserve evaluation.

If you are due for colorectal cancer screening, ask your doctor which test is right for you. Screening guidelines generally recommend starting at age 45 for most adults at average risk. People with a family history or other risk factors may need to start earlier.

A proctosigmoidoscopy is one option among several. Understanding what it can and cannot do helps you make a more informed decision with your doctor.