The PSA Test - How Does It Work

The purpose of this article is to remove some of the mystery surrounding the PSA test and its use in signaling the potential presence of prostate cancer.

The cells of the prostate gland produce prostate-specific antigen. A rectal exam and a PSA (prostate-specific antigen) test will help detect prostate cancer in men age 50 or over. The Federal Drug Administration approved the use of the PSA test to detect prostate cancer and to see if the cancer has recurred. A high PSA level is a sign that cancer is present. There are other reasons for a high PSA level and PSA screening has some limits.

The PSA test measures the level of protein produced by the prostate gland. The doctor will take a blood sample and send it to a laboratory. This test is sometimes called a biological marker for cancer tumors. Men normally have low levels of PSA in their blood. If the rate is high, it could point to prostate cancer but it can mean there are other non-cancer conditions present in the prostate. As men get older, prostate cancer and other prostate problems become more of a problem. Enlarged prostate and prostatitis may raise the PSA levels in the blood. Neither of these problems causes cancer but it is possible for a man with one of these problems to develop prostate cancer.

The PSA level will not tell the doctor if the patient has a benign prostate problem or cancer. The doctor will use the PSA test to decide if there should be a check for other signs of prostate cancer.

The Federal Drug Administration approved the PSA test to be used with a rectal exam to check for any abnormalities in the prostate. The doctor will insert a gloved finger into the rectum to check for lumps or areas that seem abnormal. The PSA test is used with this rectal exam to detect cancer in men, especially those who have no symptoms. The FDA also approved the test for patients who have had prostate cancer to see if the cancer has come back.

The PSA test is highly recommended for men over the age of 50. If the patient has a high risk factor for prostate cancer, the doctor may recommend PSA testing to start at age 45. There are some risk factors a man should look at if a doctor recommends routine screening. Age is the most common risk factor, but if there is a family history of prostate cancer you have a greater chance of having it too. African-American has the largest risk of contacting prostate cancer. Native American and Asian men have the lowest rates of this disease. Some think this might be because a diet that is high in animal fat may increase the chance of getting prostate cancer.

If a man shows a high PSA level in his blood the doctor may look for other causes before doing more screening for prostate cancer. If the patients have no other symptoms, you may be advised to watch for any changes in urination habits and take another PSA test in a few months.

So, in summary, pros and cons of the PSA test?

Possible benefits of having the test

* It may provide reassurance if the test result is normal.

* It can help to detect prostate cancer before any symptoms develop.

* Treatment in the early stages of prostate cancer could help you live longer and avoid the complications of cancer (although there is no good evidence that this is so).

Possible disadvantages

* It might detect a slow-growing cancer that may never cause any symptoms or shorten your life span. But the diagnosis of 'cancer' may cause you significant anxiety which could affect your quality of life.

* It may lead you to have treatment for early prostate cancer which might not help you live longer. Also, the main treatments for early prostate cancer do carry some risk and can cause side-effects.

* It could miss cancer in the prostate, and falsely reassure you that all is well.

* It could lead to anxiety and a biopsy when you have no cancer.

Ultimately, the decision should be taken by yourself in conjunction with your GP who can advise further and who knows your particular circumstances.

Prostate-Specific Antigen (PSA) Blood Test

Prostate-specific antigen (PSA) is a substance produced by the prostate gland. Elevated PSA levels may indicate prostate cancer or a noncancerous condition such as prostatitis or an enlarged prostate.

Most men have PSA levels under four (ng/mL) and this has traditionally been used as the cutoff for concern about risk of prostate cancer. Men with prostate cancer often have PSA levels higher than four, although cancer is a possibility at any PSA level. According to published reports, men who have a prostate gland that feels normal on examination and a PSA less than four have a 15% chance of having prostate cancer. Those with a PSA between four and 10 have a 25% chance of having prostate cancer and if the PSA is higher than 10, the risk increases to 67%.

In the past, most experts viewed PSA levels less than 4 ng/mL as normal. Due to the findings from more recent studies, some recommend lowering the cutoff levels that determine if a PSA value is normal or elevated. Some researchers encourage using less than 2.5 or 3 ng/mL as a cutoff for normal values, particularly in younger patients. Younger patients tend to have smaller prostates and lower PSA values, so any elevation of the PSA in younger men above 2.5 ng/mL is a cause for concern.

Just as important as the PSA number is the trend of that number (whether it is going up, how quickly, and over what period of time). It is important to understand that the PSA test is not perfect. Most men with elevated PSA levels have noncancerous prostate enlargement, which is a normal part of aging. Conversely, low levels of PSA in the bloodstream do not rule out the possibility of prostate cancer. However, most cases of early prostate cancer are found by a PSA blood test.

How Is The PSA Screening Test Done?

The test involves drawing blood, usually from the arm. The results are usually sent to a laboratory and most often come back within several days.

When Should I Have My PSA Levels Tested?

PSA blood tests and digital rectal exams should be done every year for men beginning at age 50, and earlier (age 40) for African American men and men with a family history of prostate cancer.

If your doctor is concerned that you might have prostate cancer based on either your PSA level or a rectal exam, a biopsy (a lab testing of a small amount of tissue from the prostate) will be this next step This is the only way to positively identify the presence of cancer.

What does the PSA test tell me about my prostate?

A raised PSA level can be a sign that you have prostate cancer. The PSA level is often raised well before any symptoms of prostate cancer develop. So the test can help to detect early prostate cancers (which may have a better chance of being successfully treated than more advanced prostate cancers.) As a rule, the higher the PSA level, the more likely that you have prostate cancer.

However, a raised PSA level can also occur in other prostate conditions such as some cases of benign enlargement of the prostate and inflammation of the prostate (prostatitis). In particular, a PSA level that is mildly or moderately raised has a good chance of being due to a benign condition, but could be due to prostate cancer. Overall, about 2 in 3 men with a raised PSA level do not have prostate cancer.

Also, if you do have prostate cancer, a single PSA test cannot tell you whether a prostate cancer is slow or fast growing.

And also, in some cases, the PSA level may be normal even when there is cancer there. Up to 1 in 5 men with prostate cancer have a normal PSA level.

So, the PSA test is not an accurate test for prostate cancer.

What conditions other than cancer cause the PSA level to rise?

The prostate typically enlarges as men grow older, and because small amounts of PSA are produced by the healthy prostate, its blood level tends to rise. Benign prostate enlargement (a condition which causes urinary symptoms such as poor flow, getting up at night), is a common non-cancer condition causing PSA levels to rise. For this reason, age-based thresholds, shown in Table 1, can be used to decide if a test result is abnormal. The percentage Free to Total PSA (described below) also gives an indication whether raised PSA is due to benign enlargement.

A temporary rise in the PSA can be caused by a number of conditions 1. Urinary infection, prostatitis (inflammation of the prostate), or a biopsy of the prostate can cause large rises while small rises can be caused by ejaculation and even bicycle riding. Because of these non-cancer causes of PSA rises, it is not surprising that if you have an abnormally high test result, it may not be due to prostate cancer. The chance that you have prostate cancer is only about one in three.

Table 1 - Suggested upper limits of PSA for different age groups 2

Age (years) Serum PSA (ng/ml)

40 - 49 2.0

50 - 59 3.0

60 - 69 4.0

70 - 79 5.5

Note: These levels are used only as a guide. It is possible to have prostate cancer and have a PSA level in the normal range, although this is uncommon.

If, in addition to the PSA test, you have a rectal examination, and it also is abnormal, your chances of having prostate cancer are higher, (one in two).

Other ways of measuring PSA have been developed in an effort to make the test more specific for prostate cancer. One of these is called the "Free to Total" PSA. This is a ratio, expressed as a percent. Much of the PSA in the blood is bound to protein, including that produced by cancer cells. But men with benign prostate enlargement have higher levels of free (unbound) PSA and so a higher Free to Total ratio. If the total PSA level is abnormal, the Free to Total PSA ratio will give an idea of whether the rise is due to benign disease or cancer. Cancer is more likely if the Free to Total percentage is below 10% 2. This test is available and widely used throughout Australia.