Prostate Specific Antigen (PSA)

Graph showing the PSA ratio and the risk of prostate cancer

Graph – Prostate Specific Antigen Ratio for Prostate Cancer testing
Image by Ryanjo (CC BY-SA 3.0)

What is PSA?

A test for the prostate specific antigen (PSA) can be used to follow the success of treatment for prostate cancer and infection. If the levels drop, treatment is successful; if they increase, it is not.

There has been a lot of controversy about the use of this test as a screening test for prostate cancer. It has been argued that early detection leads to more effective treatment, and in younger men this is true, but it is a rare disease under 50 years of age. In older men, early detection does not necessarily mean a better outcome, as some cancers are dormant and do not need treatment, the treatment may have significant side effects, and some cancers are incurable even with radical treatment.

A level of PSA below 4 micrograms per litre is usually normal, while a level over 10 is probably due to cancer, but unfortunately, many conditions other than cancer can cause the results to be high (eg. infection or enlargement of the gland). Low levels may be present in obese men despite the presence of prostate cancer.

A combination of tests for different types of PSA (free and total PSA) may be a better form of screening, but is still quite expensive. A free/total ratio of more than 25% is normal, while lower ratios are more likely to be associated with prostate gland cancer. It is only appropriate to use this ratio when the PSA is greater than 4 µg/L. The ratio between the amount of PSA free in the blood and the amount bound to proteins is measured.

False positive and false negative results are also possible. Approximately 20% of men with prostate cancer do not have a raised PSA, while another 20% with a raised PSA do not have prostate cancer. As a result it is not an absolute test for prostate cancer. As a result a regular screening PSA test is not recommended as part of an annual check-up for men.

On the other hand, if a man has symptoms of prostate disease (eg. difficulty in passing urine, difficulty in starting the urine stream, blood in the urine or semen, impotence, pain behind the base of the penis) or a bad family history of prostate cancer, a PSA test is adviseable.

Advantages of PSA testing

  • side effects of treatment are fewer with early treatment of prostate cancer
  • PSA increases the chance of detecting prostate cancer early
  • modern treatment is often successful in curing early cancers
  • most cancers detected with PSA are serious
  • a low level of PSA is reassuring

Disadvantages of PSA testing

  • a raised PSA result may be due to other conditions other than cancer
  • some prostate cancers are not serious and may be treated excessively
  • a cure cannot be guaranteed with early detection
  • there may be significant side effects from treatment
  • the investigation of the raised PSA by biopsy can cause serious complications
  • the treatment of prostate cancer is not straight forward and may lead to significant patient stress and confusion.

For men over 70 years, knowing they have prostate cancer can have more serious consequences than not knowing it is there, as the benefits of treatment may be very limited.

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