Comparing PSA and Digital Exams to Diagnose Prostate Cancer

Why You Can't Have One Without the Other

Close-up of a patient dreading an examination. Credit: rubberball / Getty Images

When it comes to screening for prostate cancer, men can sometimes be squeamish about getting a digital rectal exam (DRE), a relatively simple procedure in which a finger is inserted into the rectum. Some will even ask why the blood test, called the prostate-specific antigen (PSA), is not enough to diagnose the condition.

Ultimately, it is not possible to pick and choose between the two exams as each serves its own particular purpose.

However unpleasant and uncomfortable it may seem, the DRE remains a vital tool in helping doctors obtain a definitive diagnosis of cancer.

Understanding the DRE and PSA

The purpose of the DRE and PSA is to catch prostate cancer early before symptoms appear and it has that chance to spread to other parts of your body. While prostate cancer remains one of the most treatable of all cancers, early diagnosis offers you the best chance of a complete cure.

DRE (digital rectal exam)

PSA (prostate-specific antigen)

The doctor places a gloved finger into the rectum to feel the prostate gland.

A small amount of blood is drawn from the arm and tested in a lab.

The DRE checks for lumps, swelling, tenderness, hard spots, and other abnormalities of the prostate gland.

Elevated PSA levels indicate there are changes to the prostate which may be cancerous or benign. Levels can vary, as follows:

  • Normal: under 4 ng/mL
  • High: over 10 ng/mL
  • Intermediate: between 4 and 10 ng/mL

Limitations of the PSA

Prostate-specific antigen is a protein produced by the prostate gland. Prostate cells are tasked with keeping semen in a liquid state so that sperm can swim. If the prostrate has any problems, the PSA levels will rise in response.

While valuable, a PSA test only hints at a problem rather than diagnoses one.

PSA levels can be elevated for any number of reasons, and some men with prostate cancer may even have low PSAs. Obesity, for example, can throw off PSA readings as an overweight person has larger blood volumes that can dilute the protein

False positives and false negatives are also known to occur, which is why the U.S. Preventive Services Task Force (USPSTF) gave the test a provisional "C" rating, indicating that it should never be used on its own to diagnose prostate cancer.

How the PSA and DRE Help Diagnose Prostate Cancer

Think of the PSA as the first knock on the door that something is worrisome. Instead of skipping straight to a biopsy or starting therapies you may not need (or tolerate), the DRE provides you a minimally invasive way to know whether there is a problem that needs treating.

If and only if there is, your doctor can proceed to schedule a biopsy or other procedures needed to pinpoint the cause.

If the DRE does not suggest prostate cancer, you will be advised to have routine follow-up screenings. The frequency will be determined by the results of your PSA blood test, as follows:

  • a PSA of under 2.5 ng/mL recommends testing every 2 years
  • a PSA of 2.5 ng/mL or higher recommends yearly testing

    A Word From Verywell

    It is always important that you weigh the "discomfort" of undergoing a DRE against the benefits of early care and treatment should you, in fact, have prostate cancer. The procedure is quick and easy and far less troublesome than some might lead you to believe.

    At the end of the day, don’t let a little embarrassment keep you from diagnosing a type of cancer that continues affect more than one in seven American men.

    Sources:

    Centers for Disease Control and Prevention (CDC). "What Screening Tests Are There for Prostate Cancer?" Atlanta, Georgia; updated July 18, 2015.

    U.S. Preventive Services Task Force (USPSTF). "Prostate Cancer: Screening." Rockville, Maryland; May 2012.

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