Prostate specific antigen (PSA)

Prostate specific antigen (PSA) facts

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  The PSA test is a blood test.

  
  


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  The PSA test can be used to suggest the presence of or monitor prostate cancer.

  
  


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  The PSA test can be abnormal with benign enlargement and infection of the prostate gland.

  
  


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  The PSA test can be elevated with other conditions that irritate the prostate gland.

  
  

What is prostate specific antigen?

Prostate specific antigen (PSA) is a substance produced almost exclusively by certain cells within the prostate gland. Biochemically, it belongs to the protease family of kallikrein and is also known as human kallikrein 3 (hK3). PSA is secreted by the prostate in the semen where its role is to liquefy the semen following ejaculation. Most of the PSA produced by the prostate gland is carried out of the body in semen, but a very small amount escapes into the blood stream, so PSA is normally found in low amounts (nanograms per milliliter or ng/mL) in the blood.

If the PSA level is high for your age or is steadily increasing (with or without an abnormal physical exam), a biopsy may be recommended. The doctor should consider other risk factors of prostate cancer such as family history and ethnicity before recommending the biopsy. The biopsy is the only way to determine if prostate cancer or other abnormal cells are present in the prostate.

How is PSA measured?

PSA is measured by a blood test. Since the amount of PSA in the blood is very low, detection of it requires a very sensitive type of technology (monoclonal antibody technique). The PSA protein can exist in the blood by itself (known as free PSA), or bound with other substances (known as bound or complexed PSA). Total PSA is the sum of the free and the bound forms. The total PSA is what is measured with the standard PSA test.

What causes PSA elevation in the blood?

It is believed that elevation of PSA in the blood is due to its liberation into the circulation because of disruption of the prostate cellular architecture (structure). This can occur in the setting of different prostate diseases including prostate cancer. It is important to note that PSA is not specific to prostate cancer but to prostatic tissue and therefore PSA elevations may indicate the presence of any kind of prostate disease. The most common cause of PSA elevation includes benign prostatic hyperplasia (BPH = enlargement of the prostate, secondary to a noncancerous proliferation of prostate gland cells) andprostatitis (inflammation of the prostate). In fact, PSA elevation can also occur with prostate manipulation such as ejaculation, prostate examination, urinary retention or catheter placement, and prostate biopsy. As such, men choosing to undergo PSA testing should be aware of these important factors, which may influence results. Age and prostate volume may also influence PSA test results. 

What are normal results for the PSA test?

The “normal” PSA serum concentration ranges between 1.0 and 4.0 ng/mL. However, since the prostate gland generally increases in size and produces more PSA with increasing age, it is normal to have lower levels in young men and higher levels in older men. The PSA level also depends on ethnicity and family history of prostate cancer. Other than the single reading, the changes in PSA numbers on an annual basis (also referred to as PSA-velocity) also play a role in decision making about the PSA marker. The normal increase of less than 0.75 ng/mL is used to help determine whether levels may be suggestive of disease and to counsel men on management. As such, a man under 50 to 59 years of age with an increase in PSA levels from 0.5 ng/mL to 2.5 ng/mL may cause greater concern despite the “normal” value at that time.