Prostatic Specific Antigen (PSA) is an enzyme (or chemical) produced exclusively by prostate tissue. It is a small molecule which normally is secreted into the prostate ducts where its job is to liquefy the coagulated semen after an ejaculation. Because it is small, the PSA molecule can enter the blood stream where it is easily measurable. The normal values of 0.0 to 4.0 ng/ml vary with age. The normal PSA levels from age 40-49 are 0.0-2.5; from 50-59 are 0.0-3.5; from 60-69 are 0.0 4.5; and from 70-79 are 0.0-6.5.

PSA has been found to be an extremely useful test for aiding in the detection of prostate cancer and to monitor patients after treatment of there cancer.

If PSA molecules were injected into a person's circulation, about one half of it would disappear in three days (we call this its "half-life"); all the molecules would usually be gone in about three to four weeks. For instance, prostate manipulation from massage, catheterization, cystoscopy, acute urinary retention can cause levels to artificially rise. PSA measurements should be delayed after these procedures. Also ejaculation can artificially raise the PSA value and you should wait 24 hours before drawing the blood. However, ordinary Digital Rectal Examination (DRE) of the prostate does not cause a similar rise in PSA levels.

PSA level often rise with prostate diseases such as prostatitis (an inflammation of the prostate), Benign Prostatic Hypertrophy (BPH) - the growth of prostate commonly

causing obstruction of the bladder neck in older men), and CAncer of the Prostate (CAP). PSA levels rise with prostatitis since the inflammatory process opens up the blood stream to an increased leakage of PSA from the prostatic ducts. BPH, which causes enlargement of the gland resultS in many more prostatic ducts producing PSA. In addition, the high bladder pressures necessary to push urine through the obstructing prostate squeezes more PSA into the blood stream. CAP unlike benign diseases, will invade the lymphatic and capillary circulation so that more and more PSA leaks directly into the blood stream and thus can cause rapid and progressive rises in PSA blood levels.

The difficulty in interpreting PSA levels lies in distinguishing potentially dangerous cancer of the prostate from non-threatening benign diseases such as BPH or prostatitis.

To aid in distinguishing benign from cancerous disease the physician relies heavily on other tests. For example, a digital rectal examination will the tell the physician whether the prostate is very large from BPH, while a urinalysis and prostatic secretion examination can tell whether the prostate or urine are infected. If the prostate is very large, PSA levels will frequently rise over the normal value of 4. 0 ng/ml, but rarely over 10.0 ng/ml It is this gray zone between 4.0 and 10.0 ng/ml which can be confusing because both cancer and benign disease can cause this sort of elevation.

If the prostate is benign feeling ( soft and smooth) and enlarged then a PSA level between 4.0 and 10.0 ng/ml will usually be monitored closely. If PSA levels remain stable the chances of a hidden cancer being present are decreased However, if the levels are noted to continually be rising over a period of 3, 6 or 12 months, then it will probably be necessary to perform a prostate biopsy to further check for cancer. PSA levels do often fluctuate from time to time for unknown physiologic reasons. These variances can be as much as 30 % from one test to another. Therefore measurements over regular intervals must be taken inorder to identify a true rise. One must not over react to modest elevations of PSA and this occasional variation in levels.

On the other hand, if the prostate is small and normal on rectal examination, but the PSA is elevated, we are more suspicious of a hidden cancer When a hidden cancer of the prostate is suspected, TransRectal UltraSound (TRUS) can be used to look at the entire prostate gland. TRUS not only can find some hidden cancers, but also will allow the urologist to accurately biopsy suspicious areas found on rectal examination.

Finally, whenever the prostate has an abnormality such as a nodule, a significant asymmetry of the lobes, or a very dense lobe, TRUS guided needle biopsies of the prostate are indicated. The incidence of cancer with such findings is high regardless of the PSA level.

PSA levels have great value in early diagnosis of prostate cancer, but they are equally valuable in following the course of cancer treatment. After total prostate removal , PSA is no longer produced by cancer cells and the levels should drop to near 0 (Current tests can detect and, therefore, report levels such as <0 1 and <0 2 ng/ml) PSA production also drops with successful cancer treatment by hormones or by x-ray therapy, but not to 0 since some normal prostate tissue remains to produce PSA. A good response to x-ray treatment should drop PSA levels to less than 1.0 ng/ml and hormone treatment should drop them to <4.0 ng/ml.

PSA blood levels, when combined with digital rectal examination (DRE) are a valuable tool for diagnosis and for following treatment of prostate disease. PSA or DRE alone have some value, but used together, they will not often miss a clinically significant cancer of the prostate. PSA is not a "cancer test" as some advocate and elevated levels require sophisticated interpretation by your physician.