PSA – prostate specific antigen – is measured to screen for prostate cancer, and to monitor the response to treatment in people who have prostate cancer. Rises in PSA levels can be caused by many factors and are not always due to prostate cancer. The PSA test cannot specifically test for cancer and can only show changes happening in the prostate. By itself it isn’t enough to definitively confirm or rule out prostate cancer.
What is being tested?
Blood is being tested for the level of Prostate specific antigen (PSA) it contains. PSA is a protein produced mainly by cells in the prostate, a small gland that encircles the urethra in males and produces a fluid that makes up part of semen. Most of the PSA that the prostate produces is released into this fluid, but small amounts of it are also released into the bloodstream. PSA exists in two forms in the blood: free (not bound) and complexed (cPSA, bound to other blood proteins). The most frequently used PSA test is the total PSA, which measures the sum of the free PSA and the cPSA in the blood. When a doctor orders a "PSA test," he is referring to a total PSA.
This test is used to help detect and to monitor prostate cancer. It is not a diagnostic test for prostate cancer. It is a good tool but not a perfect one, and currently there is debate on the usefulness of this test for screening asymptomatic men (see When is it requested section below). Elevated levels of PSA are associated with prostate cancer, but they may also be seen with prostatitis and benign prostatic hyperplasia (BPH). Mild to moderately increased concentrations of PSA may be seen in those of African American heritage, and levels tend to increase in all men as they age.
Recent studies have shown that there is still a small risk of prostate cancer, even if blood PSA levels are normal for age. Therefore even a normal blood PSA level does not mean that there is definitely no prostate cancer present.
The only definite way to confirm whether prostate cancer is present or not is by prostate biopsies (taking small samples of tissue).
How is it used?
PSA is measured to help detect prostate cancer, and also to monitor the response to treatment in those with prostate cancer. However many elevations of PSA are not due to prostate cancer.
When is it requested?
Using the PSA test to screen healthy men for prostate cancer is somewhat controversial and the National Health and Medical Research Council and the Royal College of General Practitioners of Australia do not recommend PSA as a screening test in men who have no symptoms and no family history of prostate cancer. This is because in many cases PSA testing detects early cancers that are extremely slow-growing and may never cause life-threatening disease - this may cause further unnecessary testing and treatment. Guidance on this issue can be found on the Prostate Cancer Foundation website and by looking at this visual decision aid. However, men who have an increased risk for prostate cancer (such as Afro-Caribbean or African-American men, and those with a family history of the disease) may wish to be screened for prostate cancer.
The total PSA test and DRE may also be ordered when a man has symptoms that could be due to prostate cancer, such as difficult, painful, and/or frequent urination, back pain, and/or pelvic pain. Since these symptoms are seen with a variety of other conditions, including infection and prostatitis, the doctor will also frequently order other tests, such as a urine culture. Some of these conditions can themselves cause temporary increases in PSA levels. If a total PSA level is elevated, a doctor may order a repeat test a few weeks later to determine whether the PSA concentrations have returned to normal.
Free PSA is sometimes requested when total PSA levels are only mildly elevated to try to differentiate between prostate cancer and other non-cancerous conditions such as BPH. It might also be requested in combination with other tests, such as the rectal examination or biopsy, to help confirm a diagnosis of prostate cancer. Once the diagnosis is made, the PSA test might also be used to help your doctor learn about how you are responding to treatment.
What does the result mean?
The 'normal' value for total PSA are age dependent but total PSA levels greater than 10.0 µg/L may indicate a high probability of prostate cancer. Levels below 10.0 µg/L but above the usual level found in elderly men may indicate BPH, a non-cancerous swelling of the prostate, or prostate cancer. BPH occurs most frequently in elderly men. Increased total PSA levels may also indicate a condition called prostatitis, which is caused by an infection. It is important to realise that an elevated PSA level does not always indicate the presence of prostate cancer.
There is some evidence that the free PSA ratio (the percent of total PSA not bound to proteins) can help predict the probability of cancer, especially in patients with total PSA levels in the 'grey-area' range of 4.0 to 10.0 µg/L. This test may also be useful in early diagnosis of disease when values are between 2.5 and 4.0 µg/L. A free-PSA test result above 25% is thought to suggest a lower risk of cancer, whereas a lower percentage suggests a higher probability of disease. This ratio may help reduce the number of unnecessary biopsies. A recent study also suggests that very low ratios of free PSA to total PSA (less than 14%) might be associated with a more aggressive form of the disease. Additional studies are ongoing.
In most cases, test results are reported as numbers rather than as 'high' or 'low', 'positive' or 'negative', or 'normal'. In order for the doctor to properly understand laboratory results it is necessary for them to know what the reference range is for a particular test. However, reference ranges can be influenced by the patient's age and sex and, amongst other things, by what drugs they are receiving, the time of day and what they have eaten. Reference ranges can also be influenced by the test method and instrument used by laboratory. To learn more about reference ranges click on the green panel below.
Is there anything else I should know?
Prostate biopsy or operations on the prostate will significantly elevate PSA levels. The blood test should be done before surgery or six weeks after.
Ejaculation and vigorous physical activity affecting the prostate, such as bicycle riding, may cause a temporary rise in PSA levels. It is also thought that a rectal examination prior to PSA testing might temporarily raise PSA levels but recent studies have not shown this to be a consistent finding. Excessive doses of some chemotherapeutic drugs, such as cyclophosphamide and methotrexate, may also increase or decrease PSA levels.
Common questions
The most common treatments are discussed elsewhere on this site.
The incidence for disease is greater among Afro-Caribbeans and African-Americans than for Caucasian men. Hence men from these ethnic groups may wish to have their PSA tested earlier than usual.
No. Sometimes cancer cells do not produce much PSA, and the test will be negative when the disease is present.
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