A PSA level of 4 nanograms per milliliter is generally considered a healthy level for men. However as of 2015, recent studies have caused some experts to recommend lowering this level to 2.5 or 3 nanograms per milliliter, especially for younger men, as WebMD explains.
PSA levels over 4 nanograms per milliliter are common in men who have prostate cancer. Cancer is possible, though less likely, even with lower numbers. Men with a PSA reading of greater than 10 nanograms per milliliter have as high as a 67 percent chance of having prostate cancer, according to WebMD. Young men with a PSA reading of 2.5 or higher should be tested for prostate cancer.