Because high levels of prostate specific antigen (PSA) are associated with prostate cancer, many people assume that the PSA test should become a male counterpart to mammograms—a general screening test that is a part of periodic physicals.

So far, however, the evidence of the test’s usefulness is ambiguous at best. PSA results are so difficult to interpret that medical experts disagree about how the tests should be used. With no consensus, expert groups from the American Cancer Society to the National Comprehensive Cancer Network to the National Cancer Institute have all drawn up their own guidelines for use of the test.

PSA is a protein secreted by the prostate as part of its normal function. Cancer can cause it to secrete high levels, but so can many other nonmalignant conditions, including prostate inflammation or a benign condition causing prostate enlargement. In addition, PSA levels may not be elevated in cancer.

The numbers associated with the test provide no certainty. A test result of less than 2.5 ng/mL would be considered low enough to be of no concern. For men with more elevated results of 2.5–4.0 ng/mL, 20–25% were found to have cancer on follow-up. For those with higher results, of 4.0–10 ng/mL, 30–35% had cancer. And of men with the highest levels, greater than 10 ng/mL, 67% were found to have cancer on follow-up. Thus, even for men with the highest levels, a third do not have cancer, and in the “elevated” range between 4.0 and 10, two-thirds do not have cancer. A further complicating factor is that the PSA level increases with age.

Even so, isn’t it better to know that there is a chance you have cancer? Not necessarily. Prostate cancer generally grows so slowly that even if you have it, the chances are you will die of something else before the cancer becomes noticeable. Autopsies found prostate cancer in one-third of men under the age of 80 and in two-thirds of older men. Because of this slow growth, most guidelines conclude that it is not worth screening men with a life expectancy of less than ten years.

If you have a high PSA level, the only reliable way to confirm whether you have cancer is to have a biopsy, a somewhat invasive procedure involving taking samples from the prostate gland itself. Although biopsies rarely have seriously problematic side effects, sometimes they do.

That’s why one EBM website for physicians warns, “No studies have yet proven a survival benefit with screening, though considerable data show the potential harms from aggressive treatments.”

Most guidelines stop short of routinely recommending the test, except in cases of men at high risk for prostate cancer. Instead, they recommend that doctors tell patients about the test and discuss the pros and cons. (See Screening Tests for Adults [50 and Up]: Prostate Cancer and Screening Tests for Adults [Ages 30–49]: Prostate Cancer.)

As a final confusing wrinkle, the National Comprehensive Cancer Network website notes: “Since prostate cancer testing became relatively common, the prostate cancer death rate has dropped. But it has not been proven that this is a direct result of early detection.”

The question posed by evidence-based medicine is: What do you do with that test result? How will a test result affect your care? Even though the test hasn’t been proven, many men have decided that the information it provides is something they want to know.