Prostate-Specific Antigen (PSA) Blood Test

What Is Prostate-Specific Antigen?

Prostate-specific antigen (PSA) is something made by the prostate gland. High PSA levels may be a sign of prostate cancer, a noncancerous condition such as prostatitis, or an enlarged prostate gland.

What Are Normal PSA Levels?

There’s no such thing as a normal PSA for any man at any given age, but most men with prostate cancer have a higher than normal level. In general:

  • Safe: 0 to 2.5 ng/mL
  • Safe for most: 2.6 to 4 ng/mL. Talk with your doctor about other risk factors
  • Suspicious: 4 to 10 ng/mL. There’s a 25% chance you have prostate cancer.
  • Dangerous: 10 ng/mL and above. Talk to your doctor right away. There’s a 50% chance you have prostate cancer.

How Is The PSA Screening Test Done?

The test involves taking blood, usually from your arm. The doctor will send the sample to a lab. Results most often come back within several days.

When Should I Have My PSA Levels Tested?

The first thing to do is talk to your doctor about the pros and cons of prostate cancer screening before you decide whether to be tested. Don’t get tested until you have that talk. Opinions differ about when you should do that.

The American Cancer Society says to get tested at age:

  • 40 or 45 if you’re at high risk
  • 50 if you’re at average risk

The American Urological Association suggests:

  • Under 40: No screening
  • 40 to 54: No screening if you’re at average risk. If you’re at a high risk, you and your doctor can decide.
  • 55 to 69: Screening if your doctor suggests
  • Over 70 or less than a 10-15 year life expectancy: No screening

The U.S. Preventive Services Task Force says:

If your doctor thinks you might have prostate cancer based on either a PSA level or a rectal exam, a biopsy is the next step. This is a test where the doctor takes a small amount of tissue from your prostate and sends it to a lab for tests. It’s the only way to be sure you have cancer.

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What Does a High PSA Level Mean?

High PSA levels could be a sign of prostate cancer or a different condition like prostatitis or an enlarged prostate.

Other things can affect your PSA level:

  • Age. Your PSA will normally go up slowly as you get older, even if you have no prostate problems.
  • Medications . Some drugs may affect blood PSA levels. Tell your doctor if you’re taking dutasteride (Avodart) or finasteride (Propecia or Proscar). These drugs may falsely lower PSA levels by half of what they should be.

If your PSA level is high, your doctor may suggest that you get a prostate biopsy to test for cancer.

Alternative PSA Testing

Newer PSA tests may help the doctor decide if you need a biopsy. But know that doctors don’t always agree on how to use or understand the results of these tests.

  • Percent-free PSA. PSA takes two major forms in the blood. One is attached to blood proteins. The other moves around freely. The percent-free PSA test shows how much PSA moves freely compared to the total PSA level. The amount of free PSA is lower in men with prostate cancer. If your PSA results are in the borderline range (4 to 10), a low percent-free PSA (less than 10%) means there’s about a 50% chance you have prostate cancer. You should probably have a biopsy. Some doctors suggest biopsies for men whose percent-free PSA is 20 or less.
  • PSA velocity. The PSA velocity isn’t a separate test. Instead, it’s a measure of the change in your PSA levels over time. Even when the total PSA value isn't higher than 4, a high PSA velocity (a rise of more than 0.75 ng/mL in 1 year) means you might have cancer and should consider a biopsy.
  • Urine PCA3 test. This urine test looks for a mix of genes that shows up in 50% of PSA-tested men with prostate cancer. It's another tool to decide if you need a biopsy.

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Problems With the PSA Test

There are reasons doctors don’t agree on whether you need this test:

  • Finding prostate cancer early doesn’t always protect you. The PSA test often finds small, slow-growing tumors that aren’t life-threatening. Treating them anyway, whether it’s with surgery or radiation, can expose you to harmful side effects and complications. Also, finding cancer early may not help if you have an aggressive tumor or if it spread to distant body parts before you found it.
  • The results aren’t always accurate. If you have a high level but you don’t have cancer, the test results can create a lot of worry and lead to medical procedures you don’t need. A negative result if you really do have cancer can prevent you from getting treatment you do need.

Using the PSA Blood Test After Prostate Cancer Diagnosis

Although the PSA test is used mainly to check for prostate cancer, it can also help your doctor:

  • Choose a treatment. Along with an exam and tumor stage, the PSA test can help determine how advanced a prostate cancer is. This may affect treatment options.
  • Check treatment success. After surgery or radiation, the doctor can watch your PSA level to see if the treatment worked. PSA levels normally fall if all of the cancer cells were removed or destroyed. A rising PSA level can mean that prostate cancer cells are present and your cancer has returned.

If you choose a watchful waiting approach to treatment, your PSA level can tell your doctor if the disease is progressing. If so, you’ll need to think about active treatment.

During hormone therapy, the PSA level can show how well the treatment is working and when it’s time to try another treatment.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on July 04, 2019

Sources

SOURCES: 

New England Journal Of Medicine.

American Urological Association. 

National Cancer Institute. 

American Cancer Society. 

News release, U.S. Preventive Services Task Force.

Cancer.net: “Prostate Cancer: Introduction.”

Zero - The End of Prostate Cancer: “PSA Screening.”

Cancer.gov: “Prostate-Specific Antigen (PSA) Test.”

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