Transrectal ultrasound (TRUS)

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on May 10, 2022.

A transrectal ultrasound, or TRUS, is a screening tool that captures images of the prostate gland. It may help diagnose prostate cancer, which is the second-most common type of cancer among men in the United States, according to the U.S. Centers for Disease Control and Prevention.

Prostate cancer grows slowly, which means it may not cause noticeable symptoms in the early stages. Doctor and patient may decide together whether to proceed with prostate cancer screening, depending on age, level of risk, and family history. Preliminary screening tests for prostate cancer may include a physical exam and a digital rectal exam (DRE), where the doctor inserts a gloved finger into the rectum in order to locate any lumps or hard areas on the prostate.

If the doctor finds anything concerning during the exam, or if the patient is experiencing prostate cancer symptoms, additional testing may be recommended. Symptoms of prostate cancer include:

  • Pain or difficulty urinating
  • Erectile dysfunction
  • Pain with ejaculation
  • Blood in the urine or semen
  • Difficulty starting and stopping urination, or higher frequency of urination

Doctors may also use a prostate-specific antigen (PSA) blood test to determine whether further testing is needed.

Men with a PSA level between four and 10 have about a 25 percent chance of developing prostate cancer, and a PSA level greater than 10 raises the risk to more than 50 percent, according to the American Cancer Society. If the PSA level in the blood is high, doctors may order a TRUS.

What is a TRUS procedure?

During a transrectal ultrasound, a small probe about the size of a finger is inserted into the rectum to produce sonogram images of the prostate. Doctors may use these images to determine whether a biopsy is needed and, if so, to ensure a tissue sample is taken from the correct place. This is called a transrectal ultrasound guided prostate biopsy. Unlike other types of imaging that use radiation to take pictures of internal organs, a transrectal ultrasound’s probe emits sound waves that bounce off surrounding tissues, and a computer makes real-time images of the area, which the doctor is able to view on an attached screen.

What is a transrectal ultrasound for?

A TRUS may help doctors not only make a diagnosis, but identify the exact location and size of a tumor as well.

A TRUS may be useful:

  • If your PSA blood test results are abnormal, or your doctor feels an abnormal area during a digital rectal exam.
  • If your doctor needs to perform a biopsy. A TRUS may help pinpoint where a tissue sample should be taken from, to give your doctor the best diagnostic results possible.
  • To help your doctor determine the size of your prostate gland, especially if it’s naturally large.
  • To help your doctor determine whether cancer has spread to any lymph nodes or other tissues.
  • To help your doctor better navigate during certain prostate cancer treatments. A TRUS may help guide procedures such as a brachytherapy (internal radiation) or cryotherapy, which freezes prostate cancer cells.

How to prepare for a transrectal ultrasound

  • Remove all jewelry.
  • Avoid blood thinners, including aspirin, seven to 10 days before the procedure.
  • If directed, use an enema to clean out the rectum two to four hours before the procedure.
  • Wear loose clothing on the day of the transrectal ultrasound.
  • Inform doctors about any allergies to medications.

What to expect during a transrectal ultrasound

A TRUS is a minimally invasive procedure performed by a radiologist to obtain ultrasound images of the prostate. In its entirety, it takes about 10 minutes to perform.

You may expect the following steps to occur during a TRUS:

  • You’ll be asked to empty your bladder and change into a gown.
  • Next, you’ll be asked to lie on your side with your knees bent up toward your chest.
  • A protective cover and lubricant will be placed over the small probe.
  • The probe will be inserted into your rectum. You may feel some pressure, but you shouldn’t feel pain.
  • Images of your prostate and nearby tissues and organs will appear on the screen connected to the probe.
  • A tissue sample or biopsy may be taken. This should cause only minimal discomfort (a numbing agent will be used).
  • It’s normal to see a small amount of blood in your semen or urine after the procedure.

Possible risks and side effects

A transrectal ultrasound is a safe way to diagnose prostate cancer. Major complications are rare, but you may experience minor side effects, including:

  • Minor rectal bleeding
  • A small amount of blood in semen or urine
  • Fever caused by infection
  • Pain and discomfort in the rectum

For a prostate biopsy, your doctor will likely prescribe an antibiotic for you to take before and for a few days afterward, in order to decrease the risk of infection. If you’re experiencing any serious side effects, notify your care team.

What happens next

A radiologist will interpret your test results by analyzing the images taken during the TRUS and share it with the doctor who ordered the test. Using this data, your doctor may recommend a follow-up exam to determine next steps.

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