Controversy surrounds the usefulness of the prostate serum antigen (PSA) test for prostate cancer screening and the interpretation of its results. Factors such as age, race, medical history and even the type of PSA test used can greatly affect the results and muddle the interpretation. In general, though, your doctor might recommend a prostate biopsy if your PSA level is higher than 4.0 nanograms per milliliter (ng/ml).
Your prostate normally produces prostate serum antigen (PSA) and secretes it into the blood. High levels of PSA in your blood can indicate a problem with your prostate, with prostate cancer as one possibility. Doctors and professional societies disagree among themselves about the value of the PSA test as a screening tool for prostate cancer because the levels of PSA often do not correlate well with your actual risk for prostate cancer. According to the National Cancer Institute, low levels of PSA do not completely rule out prostate cancer, and high levels alone do not reliably predict prostate cancer often enough to justify a follow-up prostate biopsy.
According to the American Urological Association, median values of PSA increase with age in healthy men as follows: in the 40s, 0.7 ng/ml; in the 50s, 0.9 ng/ml; in the 60s, 1.2 ng/ml; and in the 70s, 1.5 ng/ml. Based on these median values, some doctors establish age-based cutoff values for "normal" PSA levels. For example, the American Urological Association states that healthy men in their 40s have a PSA level of 2.5 ng/ml or less. A higher level, when considered with other factors, suggests the need for a biopsy.
The simplistic guideline for PSA results sets 4 ng/ml as the cutoff point for prostate cancer screening. Above this level, after considering other factors such as the results of a digital rectal exam, your age, health and life expectancy, and other symptoms, your doctor might suggest a prostate biopsy. The American Urological Association recommends confirming "low abnormal" PSA levels of 5 to 6 ng/ml before proceeding to a biopsy if your digital rectal exam was normal.
Your doctor might correct your PSA levels by a factor based on your age, or he might want to measure changes in your PSA level over time (PSA velocity or PSAV) to see how quickly your PSA levels increase. For baseline PSA levels of less than 4 ng/ml, the normal cutoff is an increase of 0.4 ng/ml per year. For baseline PSA levels of 4 to 10 ng/ml, the normal cutoff is an increase of 0.75 ng/ml per year. However, the American Urological Association reports that the PSAV does not predict biopsy outcome any better than a standard PSA test.
A high PSA level does not mean that you have cancer, and a low level does not mean that you definitely do not. According to the Mayo Clinic, about 75% of men who have a biopsy on the basis of a high PSA level do not have prostate cancer. You and your doctor should carefully consider the results of your PSA test along with other factors before deciding if you need a prostate biopsy.