PSA (prostate-specific antigen) is a substance made by the prostate gland. Although PSA is mostly found in semen, a small amount is also found in the blood. Most healthy men have levels under 4 ng/mL (nanograms per milliliter) of blood. The chance of having prostate cancer goes up as the PSA level goes up. If your level is between 4 and 10, you have about a 1 in 4 chance of having prostate cancer. If it is above 10, your chance is over 50%. But some men with a PSA below 4 can also have prostate cancer.
Factors other than cancer can also cause the PSA level to go up, including:
- An enlarged prostate like BPH (benign prostatic hyperplasia--not cancer), that many men get as they grow older.
- Age: PSA levels go up slowly as you get older, even if you have no prostate changes.
- Infection or inflammation of the prostate gland (prostatitis).
- Ejaculation can cause the PSA to go up for a short time, and then go down again.
- Riding a bicycle
- Certain urology tests
Some things can cause PSA levels to go down, even when cancer is present:
- Certain medicines used to treat BPH or urinary symptoms. You should tell your doctor if you are taking medicines for these problems, because the doctor will need to adjust the reading.
- Some herbal mixtures that are sold as dietary supplements may also hide 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 not meant for prostate health. Saw palmetto (an herb used by some men to treat BPH) does not seem to affect the measurement of PSA.
- Obesity: Very overweight men tend to have lower PSA levels.
- Aspirin: Men taking aspirin regularly tend to have lower PSA levels. This effect is most pronounced in non-smokers.