What is the PSA test?

PSA is a protein made almost exclusively by prostate cells. The PSA test measures the amount of this protein in the blood. A small but stable amount of it is always present. But the amount increases when there is some type of abnormality in the prostate. This includes cancer, but it also includes noncancerous conditions such as BPH, the age-related enlargement of the prostate, and prostatitis, an inflammation of the prostate. In fact, about two thirds of men with elevated levels do not have cancer. On the other hand, some men with prostate cancer have normal or borderline PSA results. Although the PSA test is not perfect, it is the best test currently available for early detection of prostate cancer. Since doctors started using this test, the number of prostate cancers found at an early, curable stage has increased. And since most men have normal test results, they can be reassured that they are unlikely to have prostate cancer, especially if their DRE is also negative. PSA blood test results are reported as nanograms per milliliter or ng/ml. Results under 4 ng/ml are usually considered normal. Results over 10 ng/ml are high and values between 4 and 10 are considered borderline. The higher the PSA level is, the more likely the presence of prostate cancer is. Men with a high PSA level are advised to have a biopsy, to find out whether cancer is present. Test results in the borderline range may cause some confusion. If the DRE result is abnormal, a biopsy is recommended regardless of the PSA levels. Several new types of PSA tests have been proposed to help differentiate between a borderline elevated PSA level due to BPH and one due to cancer. The percent-free PSA test appears most promising. It measures how much PSA in the blood is alone (free) and how much is bound together with other blood proteins. With cancer a lower percentage of PSA is free. Researchers estimate that this test could eliminate 20% of unnecessary biopsies in men with borderline PSA levels. The PSA velocity is also used. It measures how quickly the PSA level rises over a period of time. A faster rise (or velocity) is more indicative of cancer. But the test needs to be repeated a few times over months or years to determine velocity. Thus, this approach does not provide an immediate answer. PSA density (PSAD) is another approach that adjusts PSA for the size of the prostate, as measured by transrectal ultrasound. A higher PSAD, meaning more PSA per cubic mm or cm of prostate, indicates greater likelihood of cancer. Age-specific PSA ranges have also been proposed for PSA results. PSA levels typically rise in older men, even in the absence of cancer. Therefore, a borderline PSA result would be more worrisome for a 50-year-old man than an 80-year-old. Not all doctors agree on how to use these additional PSA tests. There are limitations to all of them. Although the main use of the PSA test is for early detection, it is also used in men diagnosed with prostate cancer. PSA testing can help predict prognosis (outlook) and guide decisions on treatment. It can be used with clinical examination results and tumor grade to help decide the probability that the tumor is confined to the prostate, and hence, curable by surgery. Men with very high PSA levels, such as greater than 20 ng/ml, are more likely to have cancer that has spread beyond the prostate and are less likely to be cured by surgery. And, after surgery or radiation, PSA can be monitored to provide an early sign that the cancer may be coming back.