It is a blood test that measures the level of Prostate-Specific Antigen (PSA), a protein secreted mainly in the prostate. The blood sample is normally taken at the GP surgery and is then sent away for analysis. The result is generally available within a week. PSA is made by the prostate gland and a raised level of PSA in the blood can be an early indication of prostate problems.
Sometimes a raised PSA level can be a sign of prostate cancer. It can also point to something less serious, such as an inflamed or infected prostate (prostatitis), or an enlargement of the prostate that often comes as men age. This is called Benign Prostatic Hyperplasia, or BPH (sometimes now called BPE, standing for benign prostate enlargement.)
Note: Be aware that raised PSA readings may be obtained if the blood sample is taken after vigorous exercise, if ejaculation has occurred in the previous 48 hours or shortly after a DRE (see next page).
The PSA test is not a foolproof test for prostate cancer – indeed it is more a measure of prostate health – but at present it is the best simple test we have. Most men (typically two out of three) who have raised PSA levels may turn out not to have prostate cancer. Worse, about one sixth of men with a ‘normal’ PSA will actually have some evidence of prostate cancer.
The older you are, the higher your PSA level is likely to be (whether or not you have prostate cancer), as PSA naturally leaches into the bloodstream with age. It is measured in nanograms per millilitre, and can range from less than 1ng/ml to readings in the 1000s. Readings from 1 to 4 (depending on age) are generally normal. A single reading is of little value, unless it is high (say over 10ng/ml). The higher the reading, the more likely it is that you have prostate cancer.
Your doctor will use the results of all the tests you have had to build up a picture of your cancer. This allows them to measure how far the cancer has spread and how quickly it may be growing.
The PSA test alone cannot diagnose prostate cancer. All men have some PSA in their blood, and the level of PSA naturally rises as men get older. The following figures are a rough guide to ‘normal’ PSA levels, depending on your age. PSA is measured in nanograms per millilitre of blood (ng/ml).
A PSA level higher than the normal range for your age may suggest a problem with the prostate. But a normal PSA result does not rule out prostate cancer. Similarly, if your PSA level is only slightly above the normal range for your age, this does not always mean that you have prostate cancer.
There is no upper limit for the PSA level, and some men may have a PSA level in the hundreds or thousands. Having a PSA level this high is uncommon but it is likely to suggest that a man has prostate cancer.
The PSA test is also an effective way of monitoring your prostate cancer after you have been diagnosed or had treatment, and can be used alongside other test results. You will have regular PSA tests as part of your follow-up after treatment.
If the reading is marginal (say 3–5 ng/ml), a repeat test should be requested, normally after 3 months, since the rate at which the PSA level may be increasing (called PSA velocity or PSA doubling time) is also a possible indicator of prostate cancer. Many clinicians recommend that all men over 50 or at special risk know and monitor their PSA regularly, and action should be taken when any substantial increase is noted.
If the PSA reading is high, or there are other indications, your GP should refer you to a urologist for further tests in order to determine if cancer is present. These tests are outlined in the next section.