• What is the Prostate Specific Antigen?
• How is PSA measured?
• What are normal results for the PSA test?
• How is PSA used to detect prostate cancer?
• What other conditions can cause an abnormal PSA level?
• What is the free PSA test?
• What are the limitations of the PSA test?
• PSA Test At A Glance

What is the Prostate Specific Antigen?

The prostate specific antigen (PSA) is a substance produced by certain cells in the prostate gland. PSA is a protein and is a part of semen that causes it to liquefy (keeps the semen watery). 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.

How is PSA measured?

PSA is tested in the blood. 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, or it can join with other substances in the blood. When it is by itself, it is known as free PSA. When it is joined with other substances, it is known as bound or complexed PSA. Total PSA is the sum of free and bound forms. This is what is measured as the standard PSA test.

What are normal results for the PSA test?

The most frequent value used as the highest normal level is 4 ng/mL (nanograms per milliliter). 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. Age-specific PSA levels are as follows (age group, upper normal): (40 - 49, 2.5), (50 - 59, 3.5), (60 - 69, 4.5), (70 - 79, 6.5). The use of age-specific PSA ranges for the detection of prostate cancer is controversial. Not all studies have agreed that this is better than simply using a level of 4 ng/mL as the highest normal value.

How is PSA used to detect prostate cancer?

The PSA test is used in two distinctly different ways with respect to detecting prostate cancer . It can be used in men who are not known to have the disease (screening or diagnostic test) and those who are known to have the disease (tumor marker or monitoring test).

As a screening or diagnostic test, an abnormal result will usually require additional testing. Levels above 4 ng/mL but less than 10 ng/mL are suspicious. However, most men who have this level of abnormality will actually not have prostate cancer. As levels increase above 10 ng/mL, the probability increases dramatically.

As a tumor marker or monitoring test, an abnormal result indicates recurrence of prostate cancer following initial therapy. For example, if the prostate gland is surgically removed (prostatectomy), and all of the cancer is contained within the gland, then the PSA should drop to zero. If on subsequent testing the PSA test is positive and shows increasing levels, then not all of the cancer was successfully removed and it has spread.

What other conditions can cause an abnormal PSA level?

Other diseases that affect the prostate gland can cause an elevated PSA. The most frequent problem is known as benign prostatic hypertrophy (enlargement) or hyperplasia (BPH). This condition is due to an increase in the size of the prostate gland that typically occurs with aging. Infection of the prostate gland (prostatitis) is another relatively common affliction that can also cause an abnormal elevation of PSA. Other conditions include poor blood supply to the prostate gland, instrumentation of the urethra (drainage tube from the bladder), urinary retention, and prostate biopsy.

What is the free PSA test?

Most of the PSA protein released into the blood becomes attached to other blood proteins. The PSA that does not become attached is known as free PSA and can be measured. It has been found that the level of free PSA is decreased in men who have prostate cancer compared to those with benign conditions. The exact level depends upon which test the laboratory uses, but generally less than 10% free PSA is suggestive of cancer. This test is most helpful when the usual PSA test is between 4 and 10 ng/mL.

What are the limitations of the PSA test?

A few percent of prostate cancers do not produce detectable increases in the blood PSA, even with advanced disease. Many early cancers will also not produce enough PSA to cause a significantly abnormal blood level. It is therefore important not to rely only on blood PSA testing.

The most useful additional test is a physical prostate examination by a doctor known as the digital rectal exam (DRE). During this examination a doctor inserts a finger into the rectum to feel the prostate for lumps, size, shape, tenderness, and hardness.

• The PSA test is a blood test.
• The PSA test can be used to suggest the presence of or monitor prostate cancer.
• The PSA test can be abnormal with benign enlargement and infection of the prostate gland.
• The PSA test can be elevated with other conditions that irritate the prostate gland.

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