About this test
The blood test that you are ordering tests for prostate specific antigen (PSA) which is a marker which can be used in screening for prostate cancer, as well as in its treatment.
Whilst the PSA test can help to detect prostate cancer earlier, it has several shortcomings when used as a screening test. Besides being elevated by prostate cancer, PSA levels can also be raised as a result of urinary tract infection, or even certain actitivies such as recent ejaculation and some forms of exercise. This means that there is a risk of PSA being elevated when no cancer is present (a false positive). For every 100 men with a high PSA result, approximately 75 of them will have a false positive result, and 25 will have a true positive (i.e. they will have prostate cancer). Currently the most reliable way of working out whether someone has a true positive or a false positive is by performing a prostate biopsy. Because the PSA test has a high false positive rate many of these prostate biopsies will prove to be unnecessary.
You should also be aware that PSA tests can cause false negative results. This means that the PSA result is in the normal range but the person has underlying prostate cancer. PSA levels can remain normal in the early stages of prostate cancer, providing false reassurance. If we test 100 men with prostate cancer then approximately 15 of them would have a normal PSA result (a false negative).
In some cases prostate cancer grows very slowly and may never cause symptoms or shorten lifespan. A significant proportion of the men who receive a true positive result may undergo surgery that they did not need.
Who is this test for?
Men over the age of 50 may benefit from having a PSA test even if they are well. If you have risk factors for prostate cancer then the age limit is lowered to 45. Risk factors include being black or having a family history of prostate cancer.
The National Institute for Clinical Excellence recommends PSA testing in men with symptoms that suggest an obstruction between the bladder and the outside world. These include:
Having to wait a long time before you start to pass urine.
The flow of urine being slow, or stopping and starting whilst you are passing urine.
Urine continuing to dribble after you thought you had finished passing urine.
Feeling that you have not completely emptied your bladder after you have finished passing urine.
Having to get up at night to pass urine.
If you are experiencing these symptoms then you should discuss them with your doctor as you are likely to need a physical examination of your prostate.