How to perform a digital rectal exam
The digital rectal exam (also referred to as the DRE) is used to evaluate the anus, distal rectum, pelvis, and prostate. More specifically, it is used to inspect for anal tumors, obtain fecal samples for a fecal occult blood test, assess the function of the anal sphincters, evaluate for the cause of rectal bleeding (such as hemorrhoids), and evaluate the prostate gland.
Review of anorectal anatomy
To understand how to perform a DRE, a brief review of anorectal anatomy is pertinent. The anus is the most distal portion of the large intestine. The anorectal junction is about 5 cm superior to the anal verge (e.g., the anal orifice). The anal verge is the most distal portion seen externally.
The anal canal is the lumen located between the anal verge and the rectum. The dentate line (e.g., the pectinate line) is about 2 cm superior to the anal verge and is in the transitional zone.
Figure 1. The anal canal is located between the anal verge and anorectal junction, and is divided into two sections by the dentate line.
The dentate line is the division between the ectoderm and endoderm mucosa, which is important because of their embryological origins. Above the dentate line, the mucosa is endoderm, has splanchnic innervation, and is insensitive to pain. Below the dentate line, the mucosa is ectoderm, has somatic innervation through the inferior rectal nerve, and is sensitive to pain.
Figure 2. The dentate line represents the junction between the endoderm and ectoderm portions of the anal canal.
The internal anal sphincter surrounds the upper two-thirds of the anal canal. It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall. The external anal sphincter surrounds the lower two-thirds of the anal canal and is a voluntary muscle.
Figure 3. The internal anal sphincter is a ring of involuntary smooth muscle that surrounds the upper two-thirds of the anal canal, and the external anal sphincter is a ring of voluntary muscle that surrounds the lower two-thirds of the anal canal.
How to perform a digital rectal exam
Start by communicating with the patient about why a DRE is necessary, what is involved, and how the exam will be performed. Prepare the patient for a little bit of discomfort with the exam.
If possible, have the patient lay on their side in the left lateral decubitus position (e.g., with their right side up). A standing rectal exam can also be performed, but it may not be as comfortable for some patients. Usually, a standing exam is only performed for a prostate examination.
To perform a DRE, put on gloves, and perform these five steps:
- Visually inspect the anus
- Palpate the anal sphincters
- Palpate the rectal wall
- Palpate the prostate (in males)
- Collect a fecal sample if indicated
Step 1: Visually inspect the anus
First, inspect the anus. Look for any external hemorrhoids, skin tags, anal fissures, discharge, drainage, and any other abnormalities.
Step 2: Palpate the anal sphincters
Use your index finger of your dominant hand and place some lubricant jelly on it. Ask the patient to take a deep breath in, exhale, and relax. Insert your index finger into the anus, with the finger facing anteriorly, which we will refer to as the six o’clock position.
Note the external anal sphincter tone. Ask the patient to bear down and feel for tightening of the sphincter against your finger.
Step 3: Palpate the rectal wall
Palpate the rectal wall for masses, nodules, and tenderness. From the six o'clock position (e.g., the anterior direction), rotate your finger clockwise to the twelve o'clock position (now in a posterior direction), and then return to the six o'clock position.
Step 4: Palpate the prostate
In males, the prostate gland lies anteriorly at the six o’clock position. Palpate the prostate gland and note the approximate size. Feel the prostate gland for tenderness, nodules, or masses.
Step 5: Collect a fecal sample if indicated
If the patient has any signs or symptoms of anemia or unintended weight loss, then a guaiac kit to test fecal matter for occult blood is indicated.
Figure 4. Steps to performing a digital rectal exam include, 1) visually inspecting the anus, 2) palpating the anal sphincters, 3) palpating the rectal wall, 4) palpating the prostate (in males), and 5) collecting a fecal sample if indicated.
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