Normal levels of prostate-specific antigen, or PSA, range from 1.0 to 4.0 nanograms per milliliter of blood, according to MedicineNet. The normal level may, however, be higher in older men and lower in young men because PSA levels increase with age.
PSA is a protein produced by certain prostate cells to liquefy semen during ejaculation, notes MedicineNet. Because the majority of PSA from the prostate gland is eliminated through semen, only a small quantity of it normally enters the blood. Elevated PSA levels in the blood may indicate prostate disease. Other than age, other factors that influence PSA levels in the blood include family history of prostate cancer and ethnicity.