Prostate specific antigen (PSA) is a protein made by cells in the prostate gland. It is found in the fluid part of semen and in blood. The PSA level is higher in people with prostate cancer. PSA is the most commonly used blood test to screen for early signs of prostate cancer. It is also used to track the effects of treatment for prostate cancer.
The PSA test alone cannot show if a man has prostate cancer. It is often done in combination with a digital rectal exam, a procedure in which the doctor inserts a lubricated finger into the rectum to feel for abnormal bumps or hard areas on the prostate. A PSA test and DRE can help doctors decide whether to recommend a biopsy.
PSA is made by cells in the prostate gland (both normal and cancerous ones). It is found mainly in semen, but a small amount is also found in the blood. The level of PSA in the blood increases in 25 to 92 percent of men with prostate cancer. In people without prostate cancer, the level of PSA in the blood is usually much lower.
A PSA test is an important tool for detecting prostate cancer in the early stages, when it is more likely to be curable. It is also used to monitor the effects of treatment for prostate cancer, such as surgery, radiation, or hormone therapy. Some prostate cancers are slow-growing and do not cause symptoms or lead to death. These symptom-free cancers can be detected by PSA tests and may not need to be treated.
There are different types of PSA tests, including a simple blood test and more complex tests that measure the level of PSA attached to certain proteins or unattached (“free”) in the blood. The percentage of free PSA may be a better indicator of the presence of cancer than the total PSA level.
Other tests may include a clot-busting drug, which can lower PSA levels in the blood, or a urine test to look for a protein that is released when prostate cells are damaged. Doctors may also order a biopsy, a minor surgery in which they remove samples of tissue from the prostate and examine them under a microscope for cancer cells.
Several studies have raised questions about the value of PSA testing for prostate cancer, especially in older men. The main reason is that prostate cancer tends to develop slowly over many years, so it’s possible that some tumors will be detected by PSA testing but won’t cause any health problems or lead to death. Other reasons for concern are the possibility of overdiagnosis — identifying cancer that does not improve health or reduce death rates and the potential psychological stress of false-positive PSA test results. In addition, a biopsy can be uncomfortable and stressful.
