What is PSA test?
PSA stands for prostate-specific antigen, a protein produced by the cells of prostate gland, a gland about the shape and size of a walnut that sits below a man’s bladder. PSA is not just an ordinary protein; it is also a marker (tumor marker) for the presence of prostate cancer, the second most common cancer in men after skin cancer. This protein is measured in PSA test, a test used to screen prostate cancer before the appearance of symptoms. The test is also used to monitor patient improvement after therapy and to learn if prostate cancer has recurred (come back).
The PSA is normally present in the blood but at very low amount. Increased PSA levels in the blood is observed in men with prostate cancer, prostatitis (prostate inflammation), and benign prostatic hyperplasia (BPH, prostate enlargement).To rule out prostitis and BPH, other diagnostic tools like digital rectal exam and prostate biopsy are ordered. In digital rectal exam, a doctor inserts a lubricated, gloved finger into the rectum to reach the prostate. He will feel or press the prostate to find if it is enlarged or has abnormal lumps. Prostate biopsy involves the removal of small tissue from the prostate gland to be examined. This procedure confirms the presence of cancer.
For whom PSA screening test be recommended?
There are several risk factors that increase a man’s chances of developing prostate cancer. These risk factors are taken into consideration when a physician recommends screening to his/her male patients.
Sixty three percent of prostate cancer cases occur in men age 65 and older; this makes age a common risk factor for prostate cancer. Doctors advise men 65 and older to get PSA test annually. Some doctors even recommend PSA test to people younger than 65 especially those at high risk.
Race is another risk factor. Statistics show that African-American men have the highest rate of prostate cancer while Native American and Asian men have the lowest rates.
Family history of prostate cancer is also a risk factor. Having a brother or father with prostate cancer increases the chance of a person of developing prostate cancer.
In addition to age, race, and family history, diet is another risk factor for prostate cancer. A diet higher in fat especially animal fat may increase the risk of prostate cancer.
How the test is performed?
A medical technician or nurse will draw blood from a vein (usually inside the elbow or the back of the hand) using a needle. The blood collects into an airtight tube or vial attached to the needle. The collected blood is turned over to the laboratory for examination. Another medical technician will measure PSA contained in the blood. The result of the examination will be given to the patient’s physician for interpretation.
Interpretation of PSA Results
The total prostate-specific antigen in the blood is usually reported in nanograms per milliliter (ng/mL) of blood but can also be reported in micrograms per liter (mcg/l). Normal PSA values may vary from lab to lab.
Because normal PSA levels seem to increase with age, doctors use age-specific ranges to evaluate the result of PSA test. According to WebMD, the normal total prostate-specific antigen (PSA) is 0-2.5 ng/mL for men age 40-49; 0-3.5 ng/mL for men age 50-59; 0-4.5 ng/mL for men age 60-69; and 0-6.5 mL for men 70-79 years old.
But the use of age-specific ranges is not favored by some doctors because their use may lead to missing or delaying the detection of prostate cancer. They prefer the use of one range for all ages. A 4.0 ng/mL PSA result has been generally considered the cut-off point. It means that if a person’s PSA is 4.0 or higher, his doctor may recommend prostate biopsy to determine the presence of cancerous tissue.
Doctors also use PSA velocity to detect prostate cancer. PSA velocity is the change in PSA levels over time. A rapid rise in PSA may indicate the presence of prostate cancer. To determine PSA velocity, a person is required to have periodic PSA test.
Limitations of PSA Test
High PSA leves doesn’t mean that a person has prostate cancer. Blood PSA can be raised by prostate inflammation (prostitis) and prostate enlargement (benign prostatic hyperplasia, BPH). Diagnostic procedures like digital rectal examination and prostate biopsy are needed to determine the presence of cancer.
PSA-lowering agents such as BPH treatment and dietary supplements for prostate health may mask the presence of cancer. Moreover, obese men tend to have lower PSA levels.
PSA test may also give false-positive result. A person with high PSA level does not automatically mean that he has cancer. In fact, about 75% of men who get biopsy after a positive PSA test don’t have prostate cancer.
If there is false-positive result, there is also false-negative result. A negative PSA result does not prove that a man has no cancer or will never develop cancer later on.
It is estimated that between 29 and 44 percent of men with prostate cancer diagnosed by PSA tests have tumors that would not result in symptoms during their lifetime. Overdiagnosis is the identification of tumors or cancers that would not likely to cause poor health or death.
Because of these limitations of PSA test, medical professionals debate whether PSA test contributes significantly in decreasing the number of deaths from prostate cancer.
- PSA test – MayoClinic
- PSA Test – Lab Tests Online
- PSA Test – National Cancer Institute
- PSA Test – WebMD
- PSA – MedlinePlus Medical Encyclopedia