Prostate Specific Antigen (PSA)

Prostate cancer is the most common cancer diagnosis in males. 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 uses two tests: 

• Digital rectal exam (DRE)- A test that checks your lower rectum, prostate, pelvis, and lower belly for cancer or other changes.
• PSA blood test- A blood test that measures levels of the the protein PSA, which is made by your prostate gland. PSA is part of ejaculate and helps increase sperm motility (sperm's ability 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 higher than normal, you can be screened for prostate cancer. A higher PSA level is likely caused by prostate cancer, but the PSA test isn't perfect. Some tumors don’t male PSA levels higher, and some other things (like benign prostatic hyperplasia [BPH] and prostatitis) can cause it to be falsely elevated (high for only a short time).

What do my PSA results mean?

The level that is "normal" for PSA is less than 4.0 nanograms per milliliter (ng/ml). If you have a total PSA level greater than 10.0 ng/ml, your risk of prostate cancer is higher. The trend of your PSA levels over time is more important than a single PSA value. 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 if you have a steady increase in your PSA level, you are more likely to have prostate cancer. 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 caused by benign conditions or prostate cancer, and to determine the likelihood of cancer and the need for a biopsy.

• The free PSA test finds the ratio between the PSA that is free in your blood and the PSA that is bound to proteins in your blood. In most men, most of the PSA is bound to proteins in the blood and the level 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 describes 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 may be directly related 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 provider may repeat the test or do other tests.

Causes of Elevated PSA

There are several conditions that can increase 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 providers. Family history, race, and health status play a big role in if and when screening should be done. Talk with your healthcare team to see if prostate cancer screening is right for you.