Prostate-specific antigen (PSA) is a substance made by cells in the prostate gland (both normal cells and cancer cells). PSA is mostly found in semen, but a small amount is also found in the blood. Most healthy men have levels under 4 nanograms per milliliter (ng/mL) of blood. The chance of having prostate cancer goes up as the PSA level goes up.
When prostate cancer develops, the PSA level usually goes above 4. Still, a level below 4 does not guarantee that a man doesn’t have cancer €“ about 15% of men with a PSA below 4 will have prostate cancer on a biopsy. Men with borderline PSA level between 4 and 10 have about a 1 in 4 chance of having prostate cancer. If the PSA is more than 10, the chance of having prostate cancer is over 50%.
If your PSA level is high, your doctor may advise either waiting a while and repeating the test, or getting a prostate biopsy to find out if you have cancer (see the section, €œWhat if the test results aren’t normal?€). Not all doctors use the same PSA cutoff point when advising whether to do a biopsy. Some may advise it if the PSA is 4 or higher, while others might recommend it at 2.5 or higher. Other factors, such as your age, race, and family history, may also come into play.
Factors that might affect PSA levels
The PSA level can also be increased by a number of factors other than prostate cancer, such as:
- An enlarged prostate: Conditions such as benign prostatic hyperplasia (BPH), a non-cancerous enlargement of the prostate that many men get as they grow older, may raise PSA levels.
- Older age: PSA levels normally go up slowly as you get older, even if you have no prostate abnormality.
- Prostatitis: This term refers to infection or inflammation of the prostate gland, which may raise PSA levels.
- Ejaculation: This can cause the PSA to go up for a short time, and then go down again. This is why some doctors suggest that men abstain from ejaculation for 2 days before testing.
- Riding a bicycle: Some studies have suggested that cycling may raise PSA levels (possibly because the seat puts pressure on the prostate), although not all studies have found this.
- Certain urologic procedures: Some procedures done in a doctor’s office that affect the prostate, such as a prostate biopsy or cystoscopy, may result in higher PSA levels for a short time. Some studies have suggested that a digital rectal exam (DRE) might raise PSA levels slightly, although other studies have not found this. Still, if both a PSA test and a DRE are being done during a doctor visit, some doctors advise having the blood drawn for the PSA before having the DRE, just in case.
- Certain medicines: Taking testosterone (or other medicines that raise testosterone levels) may cause a rise in PSA.
Some things might cause PSA levels to go down (even if cancer is present):
- Certain medicines: Certain drugs used to treat BPH or urinary symptoms, such as finasteride (Proscar or Propecia) or dutasteride (Avodart), may lower PSA levels. You should tell your doctor if you are taking these medicines because they may lower PSA levels and require the doctor to adjust the reading.
- Herbal mixtures: Some mixtures that are sold as dietary supplements may also mask a high PSA level. This is why it is important to let your doctor know if you are taking any type of supplement, even ones that are not necessarily meant for prostate health. Saw palmetto (an herb used by some men to treat BPH) does not seem to affect PSA.
- Obesity: Obese (very overweight) men tend to have lower PSA levels.
- Aspirin: Some recent research has suggested that men taking aspirin regularly may have lower PSA levels. This effect may be greater in non-smokers. More research is needed to confirm this finding. If you take aspirin regularly (such as to help prevent heart disease), talk to your doctor before you stop taking it for any reason.
For men not known to have prostate cancer, it is not always clear if lowering the PSA is helpful. In some cases the factor that lowers the PSA may also lower a man’s risk of prostate cancer. But in other cases, it might lower the PSA level without affecting a man’s risk of cancer. This could actually be harmful, if it were to lower the PSA from an abnormal level to a normal one, as it might result in not detecting a cancer. This is why it is important to talk to your doctor about anything that might affect your PSA level.
Newer types of PSA tests
Some doctors might consider using newer types of PSA tests (discussed below) to help decide if you need a prostate biopsy, but not all doctors agree on how to use these other PSA tests. If your PSA test result is not normal, ask your doctor to discuss your cancer risk and your need for further tests.
PSA occurs in 2 major forms in the blood. One form is attached to blood proteins while the other circulates free (unattached). The percent-free PSA (fPSA) is the ratio of how much PSA circulates free compared to the total PSA level. The percentage of free PSA is lower in men who have prostate cancer than in men who do not.
This test is sometimes used to help decide if you should have a prostate biopsy if your PSA results are in the borderline range (between 4 and 10). A lowerpercent-free PSA means that your likelihood of having prostate cancer is higher and you should probably have a biopsy. Many doctors recommend biopsies for men whose percent-free PSA is 10% or less, and advise that men consider a biopsy if it is between 10% and 25%. Using these cutoffs detects most cancers and helps some men avoid unnecessary prostate biopsies. This test is widely used, but not all doctors agree that 25% is the best cutoff point to decide on a biopsy, and the cutoff may change depending on PSA level.
A newer test, known as complexed PSA, directly measures the amount of PSA that is attached to other proteins (the portion of PSA that is not €œfree€). This test is done instead of checking the total and free PSA, and it could give the same amount of information as the other two done separately. Studies are now under way to see if this test provides the same level of accuracy.
The PSA velocity is not a separate test. It is a measure of how fast the PSA rises over time. Normally, PSA levels go up slowly with age. Some research has found that these levels go up faster if a man has cancer, but studies have not shown that the PSA velocity is more helpful than the PSA level itself in finding prostate cancer. For this reason, the ACS guideline does not recommend using the PSA velocity as part of screening for prostate cancer.
PSA levels are higher in men with larger prostate glands. The PSA density (PSAD) is sometimes used for men with large prostate glands to try to adjust for this. The doctor measures the volume (size) of the prostate gland with transrectal ultrasound (discussed below) and divides the PSA number by the prostate volume. A higher PSA density indicates a greater likelihood of cancer. PSA density has not been shown to be as useful as the percent-free PSA test.
Age-specific PSA ranges
PSA levels are normally higher in older men than in younger men, even when there is no cancer. A PSA result within the borderline range might be very worrisome in a 50-year-old man but cause less concern in an 80-year-old man. For this reason, some doctors have suggested comparing PSA results with results from other men of the same age.
But because the usefulness of age-specific PSA ranges is not well proven, most doctors and professional organizations (as well as the makers of the PSA tests) do not recommend their use at this time.