General Overview
There are, in fact, three different measures of prostate specific antigen (PSA) that can be carried out using a man’s blood sample. Two of these measures provide the basis for the commercially available, clinical PSA tests that are used by the laboratories to which your doctor may send your blood for testing.
- Total PSA or tPSA is the commonly used PSA level that you hear about all the time. It is a measure of all the PSA in your blood sample.
- Free PSA or fPSA is the amount of PSA in your blood that is freely circulating as a protein and that is not “bound” in any way to other proteins
- Complex PSA or cPSA is the amount of PSA in your blood that is complexed with or bound to other proteins. cPSA has no value in measuring risk for prostate cancer.
For those who like simple math:
tPSA = fPSA + cPSA
Some hospitals and specialty centers now have their own PSA testing equipment that is able to carry out a PSA test on a blood sample within about 15 minutes, so that you don’t have to wait days for the results.
The accuracy of medical tests like the PSA test are based on their sensitivity and their specificity. We aren’t going to get into a lot of detail here, but basically:
- The sensitivity of any PSA test is a measure of the proportion of men known to have prostate cancer who test positive when they are given that PSA test, and
- The specificity of a PSA test is a measure of the proportion healthy men, known not to have prostate cancer, who test negative when they are given that PSA test.
Why do you need to know this? Because the tPSA test is more sensitive than the fPSA test, but the fPSA test is more specific than the tPSA test.
“Ultrasensitive” PSA Tests
When PSA testing was first available in the 1980s and the early 1990s, the commercially available tests (such as the Yang Pros-Check® and Hybritech Tandem-R® assays) were really only able to measure PSA levels down to an accuracy of about 0.3 to 0.6 ng/mL. Thus, even if you had a very low PSA level, your doctor might only be able to tell you that your PSA was “less than 1 ng/mL.”
In the mid 1990s the second generation of PSA tests became available. These tests were capable of measuring PSA levels down to about 0.1 or 0.2 ng/mL. In other words they were about three times as accurate as the first generation of tests.
By the late 1990s a third generation of PSA tests had arrived, the truly ultrasensitive PSA tests, capable of measuring PSA levels down to 0.01 ng/mL and lower. The clinical value of these tests outside research laboratories is open to some question, but they are much more sensitive than the original PSA tests.
The So-called “PSA II” Test
The PSA II test is a test that became available in the late 1990s and which measured the relative amount of free PSA in the patient’s blood to the total PSA level. In other words:
PSA II = fPSA / tPSA
There are some data in support of the value of this test in disciminating between risk for prostate cancer and risk for benign prostatic hyperplasia.
How Your Doctor May Use These Tests
In general, the different PSA tests decribed above are used by doctors as follows:
- The standard (second generation) total PSA test is used in the early detection of prostate cancer and other prostate disorders. It is also used to monitor patients after treatment.
- The PSA II test may be used to differentiate between men with elevated PSA levels who are at risk for benign prostatic hyperplasia and men at risk for prostate cancer.
- The true (third generation) ultrasensitive total PSA test is used in some centers to monitor patients after treatment because it can indicate biochemical failure faster than second generation tPSA tests.
- The original (first-generation) PSA tests are no longer in clinical use.
THE "NEW" PROSTATE CANCER INFOLINK 