Prostate Specific Antigen (PSA)

Prostate cancer is the most common cancer diagnosis in men. Screening for prostate cancer is much more common since the development of the prostate specific antigen (PSA) blood test in the late 1980s. Screening for prostate cancer consists of two tests: a digital rectal exam (DRE) and a PSA blood test.

A PSA (prostate specific antigen) test is a blood test that measures the protein PSA, which is made by the prostate gland. PSA is part of ejaculate material and helps increase sperm motility (the ability for sperm to swim through the female reproductive system). Normal prostate tissue makes a small amount of PSA, but prostate cancer usually makes much more. By checking to see if your PSA level is elevated (higher than expected), you can be screened for prostate cancer. A higher PSA level is likely to be caused by prostate cancer, but the PSA test isn't perfect. Some tumors won’t elevate PSA, and some other things (like benign prostatic hyperplasia and prostatitis) can cause it to be falsely elevated.

What do PSA results mean?

The level considered "normal" for PSA is less than 4.0 ng/ml.  Men with a total PSA level greater than 10.0 ng/ml are at an increased risk for prostate cancer (more than a 50% chance, according to the ACS). More important than a single PSA value is the trend of the PSA over time. If the level increases over time, regardless of if it is above 4, further testing may be done to rule out cancer. Studies have shown that men who have a steady increase in their PSA are more likely to have prostate cancer, and if the rise is rapid, it is more likely to be an aggressive cancer.

There are a number of specialized PSA tests used to help figure out if an elevated PSA is due to benign conditions or prostate cancer, and to determine the likelihood of cancer and the need for a biopsy.

• The free PSA test evaluates the ratio between the PSA that is free in the blood and the PSA that is bound to proteins in the blood. In most men, the majority of PSA is bound to proteins in the blood and the percentage of free PSA is usually lower in men with prostate cancer.
• A test called complex PSA measures the bound form of PSA. The advantage is that while the free PSA test requires two tests in the laboratory, the complex test requires only one.
• The traditional PSA test is a combination of free PSA and complex PSA.
• The PSA velocity is used to describe the speed at which the PSA value increases over a series of blood tests (and time). The result is reported as an amount (ng/ml) per year. A series of three tests over a minimum of 18 months is needed to calculate a PSA velocity.
• PSA doubling time is the period of time it takes for the PSA to double.
• The PSA density is used to look at the level of PSA compared to the overall size of the prostate gland. A transrectal ultrasound is done to determine the size of the prostate, and that number is divided into the PSA value. A rise in PSA could be directly proportional to an increase in prostate size. This test is not used very often because it has not been proven to be reliable, especially when it comes to measuring the prostate volume correctly.

PSA Testing After Prostate Cancer

The PSA test is often used to monitor men after prostate cancer treatment for recurrence (the cancer coming back). This "biochemical relapse" often occurs many months or even years before physical signs of a recurrence. A single elevated PSA after treatment does not always mean there is a relapse and your healthcare team may repeat the test or do other tests to further evaluate.

Causes of Elevated PSA

There are several conditions that can increase the PSA that are not cancer, including benign prostatic hypertrophy (BPH) and prostatitis. Any irritation of the prostate can also cause an elevation. For this reason, men are asked to not ejaculate for 48 hours before the test, and the PSA level should be drawn before a digital rectal exam is done. A group of medications called 5-alpha reductase inhibitors (finasteride, dutasteride) that are used to treat BPH can cause a false reduction in the PSA level. Saw Palmetto (an herbal supplement) may also affect PSA levels.

Several studies have found that prostate cancer screening may not reduce the number of deaths due to the disease and may expose men to testing and treatment they don’t need. However, the decision to have prostate cancer screening is something each man should discuss with his healthcare team. Family history, race, and health status play a big role in when and if screening should be done. Talk with your healthcare team to see if prostate cancer screening is right for you.