A rectal biopsy is a procedure used to extract a tissue sample from the rectum for laboratory analysis. The rectum is the lowest 6 inches of the large intestine, located just above the anal canal. The rectum’s purpose is to store the body’s solid waste until it’s released.

A rectal biopsy is an important tool for determining causes of abnormalities in the rectum. It helps to diagnose problems that are identified in screening tests such as anoscopy or sigmoidoscopy.

Anoscopy and sigmoidoscopy each use a different type of scope to observe the inner lining of the colon and rectum. The tests can identify the presence of conditions such as tumors, polyps, bleeding, or inflammation.

However, these tests are limited in determining the causes of these abnormalities. Your doctor may have to order more tests before they are able to give you a diagnosis.

Your doctor may recommend a rectal biopsy to:

  • identify the cause of blood, mucus, or pus in your stool
  • determine the causes of tumors, cysts, or masses identified in a rectal screening test
  • confirm a diagnosis of amyloidosis (a condition in which abnormal proteins called amyloids build up in your organs and spread through your body)
  • make a definitive diagnosis of rectal cancer

To get the most reliable results from your rectal biopsy, it’s necessary for your doctor to see the rectum clearly. This requires that your bowels are empty. You’ll typically be given an enema or laxative to help you empty your bowels.

You should tell your doctor about any prescription or over-the-counter medications you’re taking. Discuss how they should be used before and during the test.

Your doctor may provide special instructions if you’re taking medications that could affect the procedure, especially if your biopsy is part of a sigmoidoscopy. These medications may include:

  • anticoagulants (blood thinners)
  • nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin (Bufferin) or ibuprofen (Advil)
  • any medications that affect blood clotting
  • herbal or dietary supplements

Tell your doctor if you’re pregnant, or think you might be, to ensure that your fetus isn’t harmed.

A rectal biopsy is usually performed during an anoscopy or sigmoidoscopy. These tests are outpatient procedures, meaning you’ll be able to go home afterward. They’re typically done by a gastroenterologist or surgeon.

Anoscopy

An anoscopy is typically performed in a doctor’s office. This test uses a lighted scope called an anoscope. The scope allows the doctor to view the lowest 2 inches of the anal canal and the lower rectum. A proctoscope, which is longer than an anoscope, may also be used.

Sigmoidoscopy

A sigmoidoscopy can be performed in a hospital, an outpatient surgical center, or in a specially equipped doctor’s office.

This test uses a much longer scope. A sigmoidoscope enables the doctor to see further into the large intestine, past the rectum, and into the colon. It’s a flexible, lighted tube that is over 2 feet long. It has a camera that transmits video images to a monitor. The images help the doctor guide the sigmoidoscope through the rectum and colon.

The procedure

Preparations for both types of procedures are similar. The sigmoidoscopy, which is the more complicated procedure, takes about 20 minutes to perform. Taking a rectal biopsy can slightly extend the time the procedure will take.

Typically, general anesthesia, sedatives, and painkilling medication aren’t administered for the procedures. You’ll be positioned lying on your left side on an examining table. You’ll pull your knees toward your chest.

Your doctor will perform a digital rectal examination. A lubricant will be applied to a gloved finger, which will be inserted gently into your anus. The initial exam is to check for obstructions that may interfere with the scope.

You shouldn’t feel any pain during the digital rectal examination, but you may feel pressure. Your doctor will then insert the lubricated scope. You will feel pressure when the scope is inserted, and you may feel cramping, as though you need to pass gas or have a bowel movement.

If you’re having a sigmoidoscopy, air will be inserted into the colon through the scope. This inflates the colon to allow the doctor to see the area more clearly. If fluid or stools are in the way, your doctor may use suction to remove them. You may be asked to change position to allow the doctor to alter the position of the scope.

Your doctor will remove a sample of any abnormal tissue they find in the rectum. The biopsy will be extracted with a brush, swab, suction catheter, or forceps. You shouldn’t feel pain from the tissue removal.

Electrocauterization, or heat, may be used to stop any bleeding that results from tissue being removed. When the procedure is over, the scope is removed slowly from your body.

The degree to which you need to recover will depend on the type of procedure that was used to collect your rectal biopsy.

After a flexible sigmoidoscopy, you may experience bloating from the air that was introduced into the colon. This may result in abdominal discomfort or passing gas for a few hours after the procedure.

It isn’t uncommon to find a small amount of blood in your first bowel movement after your rectal biopsy. However, you should contact your doctor if you experience:

  • extreme abdominal pain
  • fever
  • more than one bloody bowel movement, especially if bleeding is heavy or clotted
  • a feeling of faintness

You can resume your normal diet and activities as soon as the procedure is over.

A rectal biopsy can provide valuable data for diagnosing abnormal tissue in the rectum. In cases where cancer is a concern, the procedure can provide a definitive diagnosis.

However, a rectal biopsy, like any invasive procedure, carries the risk of internal damage to the targeted organ or nearby areas. Potential risks of a rectal biopsy include:

These risks are very rare.

The tissue sample that was retrieved during your rectal biopsy will be sent to a laboratory for examination. A pathologist — a doctor who specializes in disease diagnosis — will examine the tissue. A report on the findings will be sent to your doctor.

If the results of your rectal biopsy are normal, the findings will indicate the following:

  • The anus and rectum are normal in size and appearance.
  • There is no bleeding.
  • No polyps, hemorrhoids, cysts, or tumors were found.
  • No abnormalities were noted.

If the results of your rectal biopsy are abnormal, the doctor may have found:

  • amyloidosis, which involves abnormal buildup of a certain type of protein
  • abscesses
  • infection
  • inflammation
  • polyps or other abnormal growths
  • tumors

Abnormal results of your rectal biopsy also may indicate a positive diagnosis for:

Your doctor may order more laboratory tests or physical exams before they are able to reach a diagnosis.