Prostate specific antigen (PSA) is a protein made in the prostate. It is mostly secreted into the semen to make it thinner, or more watery, to help the movement of sperm, but a small amount is also released into the bloodstream. A PSA test measures the amount of prostate specific antigen in the blood.
PSA levels in the blood may be higher than normal if you have certain conditions, such as prostate infection or inflammation (prostatitis), prostate enlargement or prostate cancer.
Why is a PSA test done?
The PSA test can be used to help in the diagnosis of prostate cancer. It can also be used as a method of screening for prostate cancer in healthy men, although there is ongoing debate about its use as a screening test (see below).
PSA tests are also used to monitor prostate cancer and its treatment.
Who should have a PSA test?
Using PSA tests as screening tests to help detect prostate cancer early in men without symptoms is controversial. Guidelines developed in 2015 by the Prostate Cancer Foundation of Australia and the Cancer Council Australia recommend the following.
- Men should discuss the risks and benefits of PSA testing with their doctor before deciding whether they should have this test.
- Men at average risk of prostate cancer who decide to have PSA screening tests should be offered PSA testing every 2 years from age 50 to 69.
- Men with a family history of prostate cancer who decide to have PSA screening tests should be offered testing from a younger age (40-45 years), depending on how many close family members have been diagnosed with prostate cancer.
- For men older than 70, the harms of PSA screening tests may outweigh the benefits.
Australian health professional bodies agree that there is not enough evidence to recommend routine PSA tests in all men to screen for prostate cancer.
What are the benefits of PSA tests?
In Australia, prostate cancer is the second-most commonly diagnosed cancer in men after skin cancer, and the second highest cause of cancer-related deaths in men after lung cancer. PSA screening tests are aimed at detecting aggressive prostate cancers at an early stage – before they have caused any symptoms and when they are still curable.
If you have already been diagnosed with prostate cancer, regular PSA testing may be done to monitor the cancer. This may be as part of an ‘active surveillance’ approach — if the cancer is thought unlikely to spread or cause problems, doctors may monitor it using PSA tests and other investigations rather than treating it straight away. Alternatively, if you have had treatment for prostate cancer, PSA tests may be done to assess the effects of that treatment.
Limitations and risks of PSA tests
One limitation of PSA tests is that a high PSA level can be caused by several conditions – PSA is not specific for prostate cancer. In fact, most men with a high PSA result are found not to have prostate cancer.
Another limitation is that PSA tests cannot differentiate between slow-growing and aggressive prostate cancers. About 20-40 per cent of prostate cancers that are detected through PSA screening are found to be the slow-growing, low-risk type that would most likely never have caused harm if left untreated.
The harms of potentially unnecessary tests and treatments in these cases may outweigh the benefits. In addition, an abnormal PSA test result and the need to decide on further tests can cause significant anxiety.
False negative PSA results are also possible. This is when men who do actually have prostate cancer have a normal PSA test result.
Risks associated with further testing and treatment
If your PSA result is abnormal, you will usually be offered a biopsy test to determine whether it is caused by prostate cancer, and if so how aggressive it is. A prostate biopsy involves taking small pieces of tissue from the prostate for examination under a microscope. Risks associated with prostate biopsy include discomfort, pain and infection.
Treatments for prostate cancer are associated with side effects such as urinary incontinence, bowel problems and erectile dysfunction.
Should I have a PSA test?
If you are thinking of having a PSA test for screening purposes, you should see your GP to talk over the risks and benefits of the test — and those of further investigations or treatment if the PSA test is abnormal.
When advising you, your doctor will take into account:
- your age;
- any symptoms you have; and
- factors that can increase your risk of prostate cancer, such as a family history of prostate cancer and having had a previous abnormal PSA test or prostate biopsy.
Having the PSA test may be more worthwhile if you have risk factors for prostate cancer than if you don’t — but whether to have the test is still an individual decision. To some extent, it depends on how you feel about cancer, investigations, treatment and your overall health. Your doctor can help you clarify what’s important to you.
How is a PSA test done?
The PSA test is a simple blood test. It’s done by taking blood from a vein — usually in your arm — and sending it to the lab for analysis.
Before you have a PSA test, tell your doctor about any medicines, supplements or herbal products you are taking, as they may affect the results. One medicine in particular, finasteride (e.g. Propecia, Proscar), which is used for treating male pattern baldness and benign prostatic hypertrophy (non-cancerous prostate enlargement), can affect PSA results.
You should also tell your doctor if you have had any urinary problems or investigations of the urinary tract such as a prostate biopsy or cystoscopy in the few weeks before a PSA test is scheduled, as these can also affect the results.
As ejaculation can make PSA levels rise briefly, some doctors recommend avoiding sexual activity for 24-48 hours before a PSA test.
What if my PSA test result is abnormal?
Your doctor will interpret your PSA results on the basis of your age — PSA levels tend to increase naturally as men get older. There is no specific cut-off point between a normal and abnormal PSA result, but as a general guide, if your total PSA concentration is higher than 3 ng/mL, your doctor may offer you further tests.
Your doctor may initially recommend that the PSA test be repeated in several weeks and may request more detailed blood PSA testing (including whether PSA is ‘free’ or attached to other blood proteins – ‘bound PSA’).
Your doctor or urologist (a specialist in the urinary system and men’s reproductive organs) may perform a digital rectal examination (DRE) — an examination in which the doctor inserts a gloved finger into the rectum to feel for abnormalities in the prostate.
Your doctor or specialist may also suggest further tests, such as a biopsy of the prostate or special MRI scans. Treatment and/or follow up will depend on your test results.
Remember, there are many potential reasons for a raised PSA level, including infection, inflammation and non-cancerous enlargement of the prostate, as well as prostate cancer. Whether or not to have a PSA screening test is up to you – discuss the pros and cons, as well as your individual risk, with your doctor so that you can make an informed decision.