Prostate-specific antigen, or PSA, is a protein produced by the prostate gland that may be found in elevated levels in the blood when a person develops certain diseases of the prostate, notably prostate cancer. Prostate-specific antigen is specific, because it is present only in prostate tissue. It is not specific for prostate cancer, however, as it may also be elevated in men with benign enlargement of this organ. The PSA test has been called the “male PAP test.”
What is the purpose of a prostate-specific antigen test?
The blood test for prostate-specific antigen is used to screen older men to detect prostate cancer at an early stage, and also to monitor its response to treatment. Any routine physical exam of a man aged 50 and older should include a digital rectal examination (DRE), in which the doctor’s finger probes the surface of the prostate gland to detect any suspicious area of hardness or a tumour mass. If the examination suggests that a tumour may in fact be present or if the examiner is uncertain the logical next step is a prostate-specific antigen test.
If the prostate-specific antigen test is positive, a sample of prostate tissue (biopsy) may be taken to confirm that cancer is present. If negative, the test may be repeated immediately to confirm the diagnosis, or repeated the next year.
Many physicians today routinely do both a DRE and a PSA test each year on their older male patients, so that, if cancer does develop, it will be found at an early stage will be easier to treat. The combination of a DRE and a PSA test can detect approximately 80% of all prostate cancers.
At present, the prostate-specific antigen test is widely accepted as a way of telling whether a patient with definite cancer is responding to treatment. Because only the prostate produces prostate-specific antigen, its presence in the blood following complete removal of the prostate (radical prostatectomy) indicates that some cancer has been left behind.
Precautions for a prostate-specific antigen test
There is no physical reason not to do a prostate-specific antigen test. Although, the level of PSA usually is elevated in men with prostate cancer, it also may be abnormally high (though usually not as high) in men with non-cancerous enlargement of the prostate (benign prostatic hyperplasia or BPH).
Description of a prostate-specific antigen test
The prostate-specific antigen test is a radioimmunoassay. Any antigen causes the body to produce antibodies in an attempt to neutralize or eliminate the antigen, often a substance that harms body tissues. In the laboratory, a sample of the patient’s blood is exposed to the antibody against PSA, so that the amount of antigen (PSA) can be measured. The results generally are available the next day.
Preparation required for a prostate-specific antigen test
No special measures are needed when doing a prostate-specific antigen test other than taking the usual precautions to prevent infection at the needle puncture site.
Normal result of a prostate-specific antigen test
Each laboratory has its own normal range for prostate-specific antigen. In fact, they may redefine the normal range whenever starting to use a new batch of test chemicals.
Abnormal result of a prostate-specific antigen test
Some experts believe that more than 90% of men with prostate cancer will have an elevated prostate-specific antigen level. Others claim that as many as one-third of cancers will be missed. The amount of PSA in the blood drops when cancer is successfully treated, but rises again if the tumour recurs, especially if it spreads to other parts of the body. A new variation of the PSA test shows how much of the material is bound to other protein in the blood and how much is “free.” This procedure may be more accurate and could well indicate whether either prostate cancer or BPH is present.