PSA Test: An Introduction
Prostate-specific antigen (PSA) is a protein produced by the cells of the prostate gland. Because PSA is produced by the body and can be used to detect disease, it is sometimes called a biological marker or tumor marker.
The PSA test measures the level of PSA in the blood. The doctor takes a blood sample, and the amount of PSA is measured in a laboratory.
It is normal for men to have low levels of PSA in their blood; however, both
prostate cancer and benign (noncancerous) conditions can increase PSA levels. As men age, both benign prostate conditions and prostate cancer become more frequent. The most common benign prostate conditions are:
- Prostatitis (inflammation of the prostate)
- Benign prostatic hyperplasia (BPH) (enlargement of the prostate).
There is no evidence that prostatitis or BPH cause cancer, but it is possible for a man to have one or both of these conditions and to develop prostate cancer as well.
PSA levels alone do not give doctors enough information to distinguish between benign prostate conditions and cancer. However, the doctor will take the result of the PSA test into account when deciding whether to check further for signs of prostate cancer.
What Is the PSA Test Used For?
The U.S. Food and Drug Administration (FDA) approved the PSA test, along with a digital rectal exam (DRE), to help detect
prostate cancer in men age 50 and older. During a DRE, a doctor inserts a gloved finger into the rectum and feels the prostate gland through the rectal wall to check for bumps or abnormal areas. Doctors often use the PSA test and DRE as
prostate cancer screening tests; together, these tests can help doctors detect prostate cancer in men who have no
prostate cancer symptoms.
The FDA has also approved the PSA test to monitor patients with a history of prostate cancer to see if the cancer has come back (recurred). An elevated PSA level in a patient with a history of prostate cancer does not always mean that the cancer has come back. A man should discuss an elevated PSA level with his doctor. The doctor may recommend repeating the PSA test or performing other tests to check for evidence of recurrence.
It is important to note that a man who is receiving hormone therapy for prostate cancer may have a low PSA reading during, or immediately after, treatment. The low level may not be a true measure of PSA activity in the man's body. Men receiving hormone therapy should talk with their doctor, who may advise them to wait a few months after hormone treatment before having a PSA test.
Recommendations Regarding a PSA Test
Doctors' recommendations for prostate screening vary. Some encourage yearly prostate cancer screening for men over age 50; some advise men who are at a higher risk for prostate cancer to begin screening at age 40 or 45. Others caution against routine screening, while still others counsel men about the risks and benefits on an individual basis and encourage men to make personal decisions about screening. Currently, Medicare provides coverage for an annual PSA test for all men age 50 and older.
Several risk factors can increase a man's chances of developing prostate cancer. These factors may be taken into consideration when a doctor recommends screening. Age is the most common risk factor, with nearly 70 percent of prostate cancer cases occurring in men age 65 and older.
Other risk factors for prostate cancer include:
- Family history
- Race
- Diet (possibly).
Men who have a father or brother with prostate cancer have a greater chance of developing the condition. African-American men have the highest rate of prostate cancer, while Asian and Native American men have the lowest rates. In addition, there is some evidence that a diet higher in fat, especially animal fat, may increase the risk of prostate cancer.
Your PSA test results report the level of PSA detected in the blood. The test results are usually reported as nanograms of PSA per milliliter (ng/ml) of blood.
In the past, most doctors considered PSA values below 4.0 ng/ml to be normal. However, recent research found
prostate cancer in men with PSA levels below 4.0 ng/ml. Thus, many doctors are now using the following ranges, with some variation:
- 0 to 2.5 ng/ml is low
- 2.6 to 10 ng/ml is slightly to moderately elevated
- 10 to 19.9 ng/ml is moderately elevated
- 20 ng/ml or more is significantly elevated.
There is no specific normal or abnormal PSA level. However, the higher a man's PSA level, the more likely it is that cancer is present. However, because various factors can cause PSA levels to fluctuate, one abnormal PSA test does not necessarily indicate a need for other diagnostic tests.
When PSA levels continue to rise over time, other tests may be needed.
Elevated Levels in a PSA Test
A man should discuss elevated PSA test results with his doctor. There are many possible reasons for an elevated PSA level, including:
- Prostate cancer
- Benign prostate enlargement (BPH)
- Inflammation
- Infection
- Age
- Race.
If no other symptoms suggest cancer, the doctor may recommend repeating the digital rectal exam and PSA test regularly to watch for any changes. If a man's PSA levels have been increasing, or if a suspicious lump is detected during the digital rectal exam, the doctor may recommend other tests to determine if there is cancer or another problem in the prostate.
A urine test may be used to detect a
urinary tract infection or blood in the urine. The doctor may recommend imaging tests, such as:
- Ultrasound (a test in which high-frequency sound waves are used to obtain images of the kidneys and bladder)
- X-rays
- Cystoscopy (a procedure in which a doctor looks into the urethra and bladder through a thin, lighted tube).
Medicine or surgery may be recommended if the problem is BPH or an infection.
If cancer is suspected, a biopsy is needed to determine if cancer is present in the prostate. During a biopsy, samples of prostate tissue are removed, usually with a needle, and viewed under a microscope. The doctor may use ultrasound to view the prostate during the biopsy, but ultrasound cannot be used alone to tell if cancer is present.
Limitations of the PSA Test
There are several limitations to the PSA test:
- Detection does not always mean saving lives: Even though the PSA test can detect small tumors, finding a small tumor does not necessarily reduce a man's chances of dying from prostate cancer. A PSA test may identify slow-growing tumors that are unlikely to threaten a man's life. Also, a PSA test may not help a man with a fast-growing or aggressive cancer that has already spread to other parts of his body before being detected.
- False-positive tests: False-positive test results (also called false positives) occur when the PSA level is elevated but no cancer is actually present. False positives may lead to additional medical procedures that have potential risks and significant financial costs, and can create anxiety for the patient and his family. Most men with an elevated PSA test turn out not to have cancer; only 25 percent to 30 percent of men who have a biopsy due to elevated PSA levels actually have prostate cancer.
- False-negative tests: False-negative test results (also called false negatives) occur when the PSA level is in the normal range even though prostate cancer is actually present. Most prostate cancers are slow-growing and may exist for decades before they are large enough to cause symptoms. Subsequent PSA tests may indicate a problem before the disease progresses significantly.
Controversy Regarding the PSA Test
Using the PSA test to screen men for prostate cancer is controversial because it is not yet known if the PSA test actually saves lives. Moreover, it is not clear if the benefits of PSA screening outweigh the risks of follow-up diagnostic tests and cancer treatments.
For example, the PSA test may detect small cancers that would never become life threatening. This situation, called over-diagnosis, puts men at risk for complications from unnecessary treatment, such as surgery or radiation. The procedure used to diagnose prostate cancer (prostate biopsy) may cause side effects, including bleeding and infection.
Prostate cancer treatment may cause incontinence (inability to control urine flow) and
erectile dysfunction (erections inadequate for intercourse).
For these reasons, it is important that the benefits and risks of diagnostic procedures and treatment be taken into account when considering whether to undertake a PSA test for
prostate cancer screening.
The benefits of screening for
prostate cancer are still being studied. The National Cancer Institute (NCI) is currently conducting the Prostate, Lung, Colorectal, and
Ovarian Cancer Screening Trial, or PLCO trial, to determine if certain screening tests reduce the number of deaths from these cancers.
The digital rectal exam and PSA test are being studied to determine whether yearly screening to detect prostate cancer will decrease a man's chances of dying from the disease. Full results from this study are expected in several years. Scientists also are researching ways to distinguish between cancerous and benign conditions, as well as between slow-growing cancers and fast-growing, potentially lethal cancers.
The following points are important to keep in mind regarding a PSA test:
- Prostate-specific antigen (PSA) is a protein produced by the cells of the prostate gland. The PSA test measures the level of PSA in the blood.
- The U.S. Food and Drug Administration (FDA) approved the use of the PSA test, along with a digital rectal exam, to help detect prostate cancer in men age 50 and older. The FDA has also approved the PSA test to monitor patients with a history of prostate cancer to see if the cancer has come back (recurred).
- Doctors' recommendations for the PSA test and prostate cancer screening vary.
- The higher a man's PSA level, the more likely it is that cancer is present, but there are many other possible reasons for an elevated PSA level.
- The PSA screening test has its limitations and is still controversial.
Add this article to your Favorites
Email this article
Print