John J. Bauer, M.D., F.A.C.S.
Prostate Specific Antigen (PSA)
John J. Bauer, MD, Urologist
PSA stands for prostate specific antigen. It is a glycoprotein produced exclusively by prostate cells, therefore, is only found in patients with a prostate.
PSA is made by normal prostate cells, enlarged prostate cells and cancerous prostate cells. In fact, it is made at the same rate by all of these cells, or slightly more so by normal cells rather than by cancerous cells. The amount of PSA found in the blood stream, however, may be different and tends to be higher in patients with prostate cancer. Normally, PSA, which is formed by the prostate cells, is secreted by these cells into the prostatic fluid. In prostate cancer, the cancer often forms microscopic spheres and these spheres do not connect to the duct system. Thus, since the PSA can not get out, it "leaks" back into the bloodstream resulting in a higher level of detectable PSA in patients with prostate cancer than in patients without cancer.
At the same time, an elevated PSA does not definitely mean that cancer is present. Benign enlargement of the prostate (BPH), which frequently occurs with normal aging is the most common cause for an elevated PSA. In addition, anything which irritates the prostate may cause the PSA to leak back into the blood steam, resulting in a higher PSA value.
Entities such as:
Prostatitis: an infection of the prostate
Cystitis: a bladder infection
Catheter insertion Cystoscopy
Dilatation of the urethra
Needle biopsy of the prostate
Transrectal ultrasound exam
A DRE (Digital Rectal Exam) or feeling the prostate, however, does not alter the PSA level.
NO TEST is always diagnostic. Since most patients with slightly elevated PSA values do NOT have prostate cancer, they would not need to have a biopsy performed. Efforts at refining the PSA test over the years have been looked at trying to determine more accurately who does and who does not need to have a biopsy performed.
These methods are:
PSA DENSITY: The thought is that patients who have large prostates (benign) should have a higher PSA level than patients with a small prostate. The PSA density is calculated by dividing the blood PSA by the size of the prostate as measured by ultrasound.
PSA VELOCITY: This refers to the rise of the PSA value over time. There is some evidence that patients with prostate cancer have a faster rate of rise than patients without cancer.
AGE SPECIFIC PSA: The theory is that younger males should have smaller prostates and therefore lower PSA values and older males have larger prostates and therefore may have higher PSA values.
FREE/TOTAL PSA RATIO: PSA occurs in at least six forms -- one not bound (free or non-complexed) and five bound to some proteins (bound or complexed). The ratio is obtained by measuring the percent of free to total PSA. As a rule, more PSA is free in patients with benign disease and complexed in patients with prostate cancer.
PSA is also a very useful test to gauge the response to treatment in patients with prostate cancer, whether this is by radical surgery, radiation therapy, or hormonal manipulation.
Although the PSA blood test is very useful test not only for following patients diagnosed with prostate cancer and in helping to identify patients with prostate cancer, it is not exact enough to be used alone in the diagnosis of prostate cancer. Elevated levels do not always mean cancer. Only a biopsy of the prostate can confirm that diagnosis.