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Prostate Specific Antigen (PSA) test

The PSA test is a blood test. Men with prostate cancer can have a raised level of PSA.

What PSA is

Prostate specific antigen (PSA) is a protein produced by both normal and cancerous prostate cells. It is normal for all men to have some PSA in their blood. A high level of PSA can be a sign of cancer. But your PSA level can also be raised in prostate conditions that are not cancer (are benign) or if you have an infection.

A diagnosis of cancer is not usually made on a PSA level alone.

The PSA test

You have a blood test to check the PSA level.

When you have the test

You might have a PSA test if you have:
  • symptoms that could be caused by prostate cancer
  • asked your GP for a test

Doctors also check your PSA level as you go through prostate cancer treatment. It helps them see how well treatment is working.

Discussing the test

Your doctor should explain to you the risks and benefits of having the PSA test. They should give you enough time to talk about it with your partner or family.


PSA is usually measured in nanograms per millilitre of blood (ng/ml). There is no one PSA reading that is considered normal. The reading varies from man to man and the level increases as you get older. 

Your doctor may refer you to a specialist if your PSA is thought to be high for your age. The specialist will do a physical examination and any other symptoms you might have before they recommend taking a sample of tissue from your prostate (a biopsy).

The PSA level isn't a certain sign of whether a man may have prostate cancer. Some men have prostate cancer but have a PSA level that is normal for their age. Other men have a higher PSA level but don't have prostate cancer. 

Very high PSA levels

Some men have PSA levels in the hundreds (or even thousands) when they are diagnosed. This usually means that a prostate cancer has spread to other parts of the body.

What affects the PSA level

The PSA level can change due to things other than cancer.

Your doctor might want to rule out a urine infection before carrying out a test. If you've had a urine infection, you shouldn't have a PSA test for at least a month to 6 weeks after your treatment finishes.

Other things that affect your PSA level include:

  • ejaculation within the last 48 hours
  • having your prostate stimulated during sex within the last week
  • having a digital rectal examination before the PSA blood test
  • doing vigorous exercise, such as cycling within the last 48 hours
  • having had a prostate biopsy in the last 6 weeks

There are different guidelines about how long to wait between these activities and having a PSA test. Ask your doctor what they recommend.

Free and bound PSA

A standard PSA test measures the total PSA in the blood. But PSA has different forms. It can either be:
  • bound – attached to a protein in the blood
  • free – not attached to a protein in the blood

One test measures the levels of free and bound PSA. It is not often used in diagnosing prostate cancer. You are more likely to have it done if your standard PSA test result was borderline.


There is no screening programme for prostate cancer because we don’t have a reliable enough test to use. And using the PSA test for screening has significant risks.

If you’re over 50 and want to have a PSA test you can ask your doctor. There are risks to having this test that your doctor can discuss with you, this will help you make a decision about whether to have the test.

Last reviewed: 
06 Mar 2018
  • Advising well men aged 50 and over about the PSA test for prostate cancer: information for GPs
    Public Health England, 2016

  • Effect of prostatic massage on serum complexed prostate - specific antigen levels
    Tahran and others

    Adult Urology, 2005. Vol 66

  • PSA measurements
    British Association of Urological Surgeons, 2016

  • Scottish referral guidelines for suspected cancer

    The Scottish Government, 2014

  • Suspected cancer: recognition and referral

    The National Institute for Health and Care Excellence (NICE), 2015


  • Effect of a low-intensity PSA-based screening intervention on prostate cancer mortality: the CAP randomized clinical trial 
    Richard M Martin PhD and others
    JAMA, 2018;319(9):883-895

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