Prostate Specific Antigen (PSA)

What is PSA, and how do we measure it?

PSA stands for Prostate Specific Antigen and is a blood test that is used to screen for the presence and amount of prostate cancer. More accurately, the PSA is found in the blood's serum, which is the fluid that the red blood cells and white blood cells travel. An antigen is a medical or biological term for a substance or protein that stimulates the body to make antibodies. Prostate Specific Antigen is a protein found in the serum that is unique or specific for the prostate, both normal prostate and prostate cancer cells. In the case of prostate cancer, the PSA will reflect the presence of the tumor, wherever the cancer cells are present in the body. No other tissues or body parts can make Prostate Specific Antigen. Therefore, the PSA levels can be measured in an individual's serum and with this information we are able to follow prostate cancer.

What is the significance of the PSA if I have prostate cancer?

If a diagnosis of prostate cancer has been made by biopsy, then the PSA level can be used as a marker for the treatment of prostate cancer. Free PSA, Complex PSA (PSA-ACT), hK2 and other new PSA screening tests have no benefit over the current used PSA tests in patients who already have a diagnosis of prostate cancer. They are helpful only in screening situations in helping us determine who needs or does not need a biopsy.

After radical prostatectomy

If the prostate gland is removed (radical prostatectomy) we expect the PSA level to be unmeasurable. However the PSA report will NOT say '0' or 'zero'. If the PSA level is unmeasurable, the laboratory will say '<' or 'less than' the lowest value that a particular test can measure, for example '<0.05'. If the '<' or 'less than' is not present, it suggests that the PSA level is unmeasurable. If any PSA is measured after radical prostatectomy, then the presence of prostate cancer cells somewhere in the body has to be suspected. If the PSA level remains unmeasurable for more than five to seven years, the chances of cancer returning become very very small. Prostate cancer cells that have spread to other areas also make Prostate Specific Antigen. Even if we cannot find the areas of spread with scans or other tests, the presence of PSA means that the cancer is present. If the treatment of the cancer was with any form of radiation, chemotherapy or hormone therapy, the PSA level will not necessarily become unmeasurable. The normal prostate cells may not be destroyed and may still leak normal amounts of PSA. However, the PSA level should be stable if the treatment is working. That means a rising PSA level suggests growth of the cancer.

After radiation therapy (external beam or implant)

After any form of radiation therapy for localized prostate cancer the prostate gland is left in place. Therefore the PSA level may not become unmeasurable. This is not unexpected and reflects the presence of remaining non-cancerous prostate tissue, which also releases PSA into the blood stream. We do expect the PSA level to fall, however, to a very low level and stay there. Currently, no exact level has been established as the expected 'break-point' of success. Some use 0.5, some 1.0 and some set no exact level but say that whatever the PSA falls to after treatment is the baseline and as long as the level doesn't rise from that point on two consecutive measurements that success has been achieved. If the PSA level starts rising after radiation therapy from whatever baseline is established, the possibility of recurrence of the prostate cancer must be suspected. Whether this recurrence is in the prostate gland itself or whether it is somewhere else in the body cannot be determined by the PSA test--only that the prostate cancer cells are somewhere.

Probability of Prostate Cancer based on test results

Standard PSA level Probability of Prostate Cancer
0-2 ng/ml 1%
2-4 ng/ml 15%
4-10 ng/ml 25%
10 ng/ml 50%

PSA of 4* or less-If your PSA level has been measured for the first time is less than 4, we recommend repeating the test on a yearly basis. (* this number may be dependent on age-see above for normal values)

PSA greater than 4-If your PSA is greater than 4, than 10, we recommend a diagnostic ultrasound of your prostate done through the rectum (TransRectal Ultrasound or TRUS) with biopsies of the prostate simultaneously. If the ultrasound shows no suspicious areas, then systematic biopsies of the entire prostate are usually taken. If the ultrasound shows suspicious areas, then biopsies of the areas, along with systematic biopsies, need to be done.

PCA-3: This urine test improves upon the accuracy of prostate cancer detection. After rectal exam a urine specimen is sent for analysis. If the protein mark PCA-3 is above a certain level then prostate biopsy is required to determine if cancer is present. This newer test is more accurate than the conventional PSA and may be used in select cases to avoid repeat prostate biopsies