Screening and Diagnosis

Even with its limitation, the PSA test has increased the number of detectable early-stage and therefore treatable cancers. Because of the slow-growing nature of prostate cancer, however, it is not known whether all of these very early cancers will result in significant or life-threatening disease. It is possible that PSA screening could result in the detection of some possible cancers that would never have bothered the patient and would never have posed a threat to his life.

PSA Test Variations

To improve the accuracy of the PSA tests, particularly when PSA levels have risen to an intermediate range of between 4 and 10 ng/mL, researchers are developing methods for measuring other factors. To date, no test has emerged as clearly superior to the PSA test.

Free PSA Test. A small amount of prostate specific antigen leaks out of the prostate into the bloodstream. There, PSA can circulate without binding to other proteins and is referred to as free PSA. It can also form chemical combinations with other proteins. If cancer is present, PSA is more likely to be bound, and so there is less free PSA in circulation. The free PSA blood test, then, is a ratio of free PSA to the total PSA (free PSA plus chemically bound PSA).

The following results are used to determine if an elevated PSA level could mean cancer:

• A free-to-total PSA ratio of 20% or lower, plus total PSA levels of 4 to 10 ng/mL, are suggestive of prostate cancer. (Some experts use 25% as a cut-off, but studies suggest that using this cut-off would miss cancers in many African American and older men.)
• A free-to-total PSA level of more than 20% plus normal or even moderately elevated total PSA tend to indicate the presence of other, benign conditions, such as benign prostatic hyperplasia (but it still does not rule out cancer).

Some studies have reported that adding a test for free PSA may improve prostate cancer detection by roughly 40% and may also reduce the need for unnecessary biopsies. In addition, any cancers that the test misses would not develop into significant disease for many years, providing ample opportunity to identify them before they became serious. Not all studies support its advantages, however, compared to measuring total PSA alone, and to date there is no consensus among doctors for how it can be used.