What is PSA
Prostate-specific antigen, or PSA, is a protein produced by cells of the prostate gland. Most of the PSA leaves the prostate with the ejaculatory fluid. Some of this protein however leaks into the blood stream. The PSA test measures the level of PSA in a man’s blood. The results are reported as nanograms of PSA per milliliter (ng/mL) of blood.
What is a normal PSA test result?
There is no specific normal or abnormal level of PSA in the blood. In general, however, the higher a man’s PSA level, the more likely it is that he has prostate cancer. When a man’s PSA is higher than the 95% percentile his risk of prostate cancer is significant enough to warrant further investigation.
PSA median and 95th Percentiles
|PSA Level (ng/ml)||Risk of Prostate cancer at biopsy|
|2 – 3.9||19%|
|4 – 5.9||21%|
|6 – 7.9||29%|
|8 – 9.9||32%|
From European Randomized Study of Screening for Prostate Cancer (ERSPC).
PSA can be elevated for a number of reasons, these include:
- Age: PSA slowly increases with age
- Benign prostatic hyperplasia (BPH): In general, the large a prostate is, the higher the PSA can be.
- Infections: Infections in both the urine and prostate can elevate the PSA. Infections can be asymptomatic.
- Inflammation: Anything that irritates the prostate can elevate the PSA, common example include a prostate biopsy and an indwelling urethral catheters.
Conversely, some drugs—including finasteride (proscar) and dutasteride (duodart and avodart), which are used to treat BPH—lower a man’s PSA level. Men on these drugs only need a PSA which is half the 95th percentile to warrant further investigation.
PSA level may also vary somewhat across testing laboratories. It is therefore better to use the same laboratory to enable more accurate interpretation of PSA changes.
At what PSA level is prostate cancer likely?
The higher a man’s PSA level, the more likely it is that he has prostate cancer. However, men with a low PSA can still have prostate cancer and men with a high PSA do not necessarily have prostate cancer.
Indications for PSA testing
PSA testing can be offered to two different groups of men. The first is to ‘screen’ men. This means the PSA test is used to stratify asymptomatic men into low or high risk of prostate cancer. Men found to be in the high risk group will be offered further investigation. PSA is not the only test used to classify when as high risk for prostate cancer. An abnormal feeling prostate on rectal examination may be another reason.
The second group of men who has PSA tests are men who have already been diagnosed with prostate cancer. In this group the PSA can indicate if the cancer has responded to treatment, if the cancer is growing or if treatment needs to be started.
When to have a PSA test
Different organisations have different recommendations about who should be tested and at what age. Points to note are:
- A large European randomized screening study showed a reduced risk of prostate cancer death with PSA testing and treatment in men aged 55-69 years old.
- Men under 55 years of age are less likely to be diagnosed with prostate cancer but if they are diagnosed, they are more likely to die from prostate cancer than older men.
- Evidence demonstrates that a baseline PSA done when a man is 40 years of age, can help predict his risk of subsequently developing prostate cancer. Specifically, men with baseline PSA levels above this age group median (>0.5 ng/ml) have a greater risk of prostate cancer diagnosis during the next 20–25 yr.
- Men with risk factors for prostate cancer should be screened earlier. Risk factors include: family history of prostate or breast cancer and African or aboriginal ancestry.
- The Urological society of Australia and New Zealand (USANZ) testing policy recommend a baseline PSA at 40 years of age, with the intensity of subsequent monitoring being individualised accordingly.
- The American urological association (AUA) recommends annual PSA testing screening for men between 55-69 years of age.
- Currently, Medicare provides coverage for an annual PSA test for all Medicare-eligible men age 50 and older.
What if a screening test shows an elevated PSA level?
If history or examination suggests a non-cancerous cause for the elevated PSA, a repeat test will be offered. If no such cause is found, further investigation is recommended.
What are some of the limitations and potential harms of the PSA test for prostate cancer screening?
- PSA elevate for other causes (False positive test)Most men with an elevated PSA level turn out not to have prostate cancer; only about 25-40% of men who have a prostate biopsy due to an elevated PSA level actually have prostate cancer. A false-positive test result occurs when a man’s PSA level is elevated but no cancer is actually present. A false-positive test result may create anxiety for a man and his family and lead to additional medical procedures, such as a prostate biopsy, that can be harmful. Possible side effects of biopsies include serious infections, pain, and bleeding.
- Prostate cancer is present but the PSA is not elevated (False-negative test)A man may have prostate cancer but his PSA level may still be low. This is called a false-negative test. False-negative test results may give a man, his family, and his doctor false assurance that he does not have cancer, when he may in fact have a cancer that requires treatment.
- PSA stands for prostate specific antigen.
- PSA is (still) the best test to identify men with prostate cancer.
- Prostate cancer is the commonest cancer in men, with >20,000 men diagnosed each year.
- There are other causes of an elevated PSA, so a high level is not diagnostic of cancer but indicates the need for further investigation.
- If prostate cancer is identified early enough cure is possible.