What is the Prostate-Specific Antigen Test?
Prostate-specific antigen (PSA) is a protein produced by cells of the prostate gland. The PSA test is a blood test that measures the level of PSA in the blood. The doctor takes a blood sample, and the amount of PSA is measured in a laboratory. Because PSA is produced by the body and can be used to detect disease, it is sometimes called a biological marker or a tumour marker.
Why is the PSA Test Performed?
The U.S. Food and Drug Administration (FDA) has approved the use of the PSA test along with a digital rectal exam (DRE) to help detect prostate cancer in men 50 years of age or 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 as these tests can help doctors detect prostate cancer in men who have no symptoms of the disease.
PSA test results show the level of PSA detected in the blood. The results are usually reported as nanograms of PSA per millilitre (ng/mL) of blood. In the past, doctors considered a PSA level below 4.0 ng/mL as normal. However, studies have shown that prostate cancer can sometimes be present in men with a PSA level at or below 4.0. Also, a PSA level above 4.0 does not mean you have cancer. There can be different reasons for an elevated PSA level besides prostate cancer, including benign prostate enlargement, inflammation, infection, age, and race.
Although 0-4.0 is usually considered normal, there is no specific normal or abnormal PSA level. Consequently, one abnormal PSA test result does not necessarily indicate the need for a prostate biopsy.
In general, the higher a man’s PSA level, the more likely it is that cancer is present. Furthermore, if a man’s PSA level continues to rise over time, other tests may be indicated.
PSA level alone does not give doctor 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.
How is PSA Test Performed?
The PSA test is a simple blood test, so there is no special preparation for this procedure.
The doctor takes a blood sample from your arm. This sample is then exposed to the antibody that attacks PSA, and the amount of PSA is measured. The normal range is around 0 - 4 ng/mL (nanograms per millilitre), but the range that is considered normal does increase with age.
If you are age 50 or older, your routine physical exam should also include a digital rectal examination. By performing a DRE, your doctor can feel the surface of the prostate gland
and check for any growths, enlargement, or tenderness. The combination of digital rectal examination and PSA testing can detect cancer at an early stage, when your treatment options are best.
Limitations of PSA Test
Detecting tumours does not always mean saving lives:
When used in screening, the PSA test can detect small tumours. However, finding a small tumour does not necessarily reduce a man's chances of dying from prostate cancer. PSA testing may identify very slow-growing tumours that are unlikely to threaten a man's life. Also, PSA testing 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 test results 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.
False-negative test results 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.