The PSA test is a blood test that measures the amount of prostate specific antigen (PSA) in your blood. It can help to diagnose prostate cancer.
Your doctor or nurse takes a sample of your blood. This can be done at your GP practice. They then send this off to a laboratory to check the amount of PSA.
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.
What is PSA?
Prostate specific antigen (PSA) is a protein produced by both normal and cancerous prostate cells. It's 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.
Discussing the test
Your doctor should explain to you the risks and benefits of having the PSA test.
The PSA level isn't always a reliable 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.
It's also only worth having a PSA test if you're well enough to have treatment if you do have prostate cancer.
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 check for any other symptoms you might have before they recommend taking a sample of tissue from your prostate (a biopsy).
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 a digital rectal examination before the PSA blood test
- doing vigorous exercise 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.
PSA velocity and density
PSA density and velocity are measures taken from your PSA blood test that can give your doctor more information about your chance of having a cancer that is likely to grow and cause you problems.
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.
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.