Prostate-specific antigen (PSA) is a protein made by the cells of the prostate gland. PSA is mostly found in semen, but it is also normal to find small amounts of PSA in the blood of healthy men. A PSA test measures the amount of PSA in the blood.
Why a PSA test is done
A PSA test may be done for 2 reasons:
- to help detect prostate cancer
- A PSA test may be done when the doctor suspects prostate cancer because of a man’s health history or the results of a physical examination.
- A PSA test may also detect early prostate cancer in men who do not have symptoms.
- Men over 50 should talk with their doctor about whether they should be tested for prostate cancer.
- Although PSA testing detects prostate cancer earlier than waiting for symptoms to appear, experts are divided about whether it is a useful test or not.
- An increased PSA level does not necessarily mean that a man has prostate cancer.
- Only about 1 in 4 men with an abnormal PSA result will actually have prostate cancer.
- The others will have a benign condition, such as prostatitis (inflammation of the prostate gland) or benign prostatic hyperplasia (BPH).
- to monitor response to cancer treatment and monitor disease recurrence or progression
- PSA acts as a tumour marker (a substance that can be found in the body when cancer is present).
- A decrease in, or return to normal values of, PSA often means that the prostate cancer has responded well to treatment. The lowest level that the PSA reaches (nadir) is used as a baseline for future PSA tests.
- The PSA level should fall to a near undetectable level (less than 0.1) in men who have been treated with surgery.
- The PSA level in men treated with radiation therapy also goes down after treatment, but because the prostate gland has not been removed, small amounts of PSA (up to 2.0) continue to be made by the benign parts of the prostate gland.
- Anincrease in PSA may mean that the cancer is not responding to treatment, is growing or has come back (recurred).
- If a man’s PSA level begins to rise, it may be the first sign of a recurrence. This may be referred to as biochemical failure or biochemical relapse. Biochemical failure is seen with repeated rises in the PSA level after it has reached its lowest level.
- A single elevated PSA measurement in a man with a history of prostate cancer does not always mean the cancer has recurred. In particular, after brachytherapybrachytherapyA type of radiation therapy that uses implants (needles, catheters, wires or seeds) to deliver radiation directly into or near a tumour. for prostate cancer, a temporary rise in PSA (PSA bounce) occurs in about half of all men, usually 1–4 years after treatment. Then the PSA level falls without any other treatment.
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Who should consider having a PSA test
Men over the age of 50 should talk to their doctor about their personal risk of developing prostate cancer and the benefits and risks of having a PSA test.
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How a PSA test is done
A PSA test is usually done in a private laboratory or hospital laboratory. A blood test is used to measure PSA.
There is no special preparation for a PSA test. However, PSA levels may be temporarily increased by:
- an inflammation of the prostate (prostatitis)
- transrectal ultrasound (TRUS) or prostate biopsy
- sexual activity
- digital rectal examination (DRE) of the prostate gland
It is recommended that a PSA test not be done for a few days after ejaculation. After a prostate biopsy or infection, the PSA can be artificially increased for up to 3 months.
Tell the doctor if you are taking drugs that may be used to treat benign prostate conditions, urinary symptoms or baldness, such as finasteride (Proscar), Propecia or dutasteride (Avodart). These drugs can decrease the PSA level.
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Benefits and risks
The PSA test can help detect prostate cancer early, but it can also cause false alarms or may miss prostate cancer when it is actually present. It is important that men talk to their doctor about their personal risk of developing prostate cancer, as well as the benefits and risks of PSA testing.
A potential benefit of the PSA test is that it will find prostate cancer early, before it grows and spreads outside the prostate. Early detection can mean that treatment will be more successful.
Potential risks of PSA testing include:
- a false-positive result
- A false-positive result suggests cancer even though no cancer is actually present.
- PSA testing has a high rate of false-positive results. Only about 1 in 4 abnormal PSA results is due to cancer.
- A false-positive result can lead to unnecessary follow-up testing that is more invasive, such as repeated biopsies.
- a false-negative result
- A false-negative result is when the PSA is normal even though cancer is present.
- The chance of a false-negative result is about 1 in 10.
- Getting a false-negative result can cause men and their doctors to ignore the symptoms of prostate cancer.
- In many cases, the PSA test may find prostate cancer that may not pose a serious threat to a man’s health. Some prostate cancers can be present for years without affecting a man’s health.
- Unnecessary follow-up testing and treatment expose men to more risks, including potentially serious side effects.
- Recent research has shown that 50% of cancers that are detected by the PSA test may never need to be treated. The majority of these men go on to have treatment, which is unnecessary in most cases.
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What the results mean
It is normal to find small amounts of PSA in the blood of healthy men. A PSA level can go up and down for different reasons. The PSA level varies with age. It tends to increase gradually in men over 60 as the prostate gland grows.
PSA is reported as a total number. Although many doctors refer to a normal PSA level being less than 4, the normal level depends very much on a man’s age. A man in his 40s will have a PSA level that is well below 4, but a man in his 70s typically has a PSA level above 4. The European Prostate Cancer Screening Trial is currently studying whether lowering the PSA level cutoff to 3 is better at detecting cancers earlier.
- The risk for prostate cancer rises with higher PSA levels.
- There is no limit to how high a PSA level may rise.
- Sometimes men with prostate cancer have a normal PSA level.
A high PSA result should be checked again before any further tests are done.
Knowing whether or not a man’s PSA level is steadily increasing or decreasing may be as important as the actual level. A jump from previous results may indicate that cancer has developed.
Reasons for higher than normal PSA levels
Many problems with the prostate can cause the PSA level to rise, so an increased level doesn’t necessarily mean a man has prostate cancer. PSA levels may be higher than normal because of:
- an enlarged prostate (benign prostatic hyperplasia or BPH)
- an inflamed or infected prostate (prostatitis)
- a recent medical test on the prostate (such as DRE, TRUS or biopsy)
- recent sexual activity (including any ejaculation)
- cancer cells in the prostate
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What happens if a change or abnormality is found
An increased PSA level can occur in non-cancerous and cancerous conditions. The doctor will decide whether further tests, procedures, follow-up care or treatment is needed. Additional tests may include:
- a repeat PSA test
- further examination of the PSA level
- serial PSA testing
- free, complexed or percent-free PSA
- PSA density
- prostate biopsy using transrectal ultrasound (TRUS)
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Other components of the PSA test
Newer tests have been developed in an attempt to refine the measurement and analysis of PSA results. These may turn out to be more accurate than regular PSA testing.
Serial PSA testing
Serial PSA tests look at changes in the PSA level over time. Serial testing is not a separate blood test, but a tracking and comparing of many PSA readings. PSA levels are known to fluctuate and can increase even when cancer isn’t present. However, men with prostate cancer will have PSA levels that rise more quickly than men who do not have prostate cancer. Serial testing is mostly used to monitor a man’s response to cancer treatment and is less useful for showing if prostate cancer is present.
Serial PSA testing calculates the PSA velocity and PSA doubling time.
- PSA velocity
- PSA velocity measures the change in PSA level over time.
- To find out the PSA velocity, at least 3 PSA test results are compared over a period of at least a year.
- If PSA velocity increases quickly, the doctor may order further tests because this may indicate cancer.
- The result is calculated as units/year (for example, a rise in the PSA of 1 µg/L/year).
- PSA doubling time
- PSA doubling time measures the time it takes the PSA level to double.
- PSA doubling time is sometimes helpful in determining which prostate cancers are likely to be aggressive or to spread.
- The result is calculated in time. For example, a PSA doubling time of 3 years means that, on average, the PSA level doubles every 3 years.
Free, complexed and percent-free PSA
PSA occurs in 2 main forms in the blood – free and complexed.
- Free PSA is not attached and circulates freely in the blood (unbound).
- Free PSA levels are often higher in benign prostate conditions.
- Complexed PSA is attached to other proteins and may be referred to as bound PSA.
- Prostate cancer cells produce more of the complexed type of PSA.
- If a man’s free PSA is low but the complexed PSA is high, cancer is more likely.
Percent-free PSA (a PSA ratio) measures the amount of free PSA compared to total PSA. Total PSA is free plus complexed PSA.
- The free-to-total PSA ratio is lower in men with prostate cancer.
- When a total PSA level (adjusted for differences in age) is between 4 and 10, testing for free PSA may be done to see if further testing, such as TRUS and prostate biopsy, should be done.
PSA density (PSAD) is the level of PSA in the blood compared to the size (volume) of the prostate measured during TRUS. PSA blood levels are usually higher in men with enlarged prostates. By comparing the PSA level to the size of the prostate, PSAD may help give a more accurate normal range for PSA levels. A high PSAD is more likely to indicate prostate cancer.
A nomogram is a tool that uses PSA results and a number of other factors (such as age, ethnicity, family history, urinary symptoms, DRE results and prostate biopsy results). It is used to:
- calculate a man’s risk of developing prostate cancer
- determine the need for a biopsy
- determine how aggressive the cancer may be
Researchers are studying the use of nomograms for assessing a man’s risk of developing prostate cancer.
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