prostate speciic antigen prostate cancer

Prostate Specific Antigen (PSA)



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Prostate specific antigen (PSA) is a protein which is produced by the normal gland and to a greater extent cancer cells. The normal blood range for PSA, depends on age and size of the gland. A normal test does not exclude prostate cancer. The upper value considered abnormal is now considered to be 4 ng/ml. Some institutions however prefer to use a ranges depending on the age::

40 - 49 years 2.5 ng/ml,
50 - 59 years 3.5 ng.ml,
60 - 69 years 4.5 ng/ml,
70 - 75 years 6.5 ng/ml

The PSA test is particularly used to [1] detect cancer and [2] to assess the response to treatment. Any man with a PSA above this age adjusted range may well wish to be transferred to a specialist Urologist for further investigation such as transrectal biopsy or MRI after considering other causes of a raised blood PSA

Cause of a raised PSA

Prostate cancer
Benign prostate hypertrophy
Infections
Recent prostate biopsies
Having a urinary catheter in (a tube to drain urine)
Prostate or bladder surgery
Prolonged exercise, such as long-distance running or cycling
Very recent ejaculation

Some drugs may also reduce the PSA level, the most well known of these are called 5alpha-reductase inhibitors. These drugs reduce the metabolism of the male hormone testosterone into active metabolites. They are given to reduce the size of a benign (non-cancerous) prostate and improve the water flow. The two most commonly prescribed are Finasteride (Proscar) and Dutasteride (Adodart).

Free versus bound PSA The PSA circulates in the blood in two forms - the free form and the form bound to a protein. Some laboratory, as well as an absolute level provide the ratio of free versus bound. The benign conditions which elevate the PSA mentioned above produce more free form whilst cancer produces more bound form. Therefore, the greater the ratio (ie more free form) to more likely that it is benign (not cancer)

The potential PSA doubling time (PSAdt)

This is the time it take the the blood PSA to double. it is sometimes referred to as the PSA velocity In many cases it hasn't actually doubled but the potential doubling time can be estimated by the following calculation. The PSAdt over any period can be calculated so you can accurately see if it shorting (bad) or lengthening (good), in response to treatments, a lifestyle programme or oral supplement such as Pomi-T®. The graph can be updated each time you get another blood test and even emailed to your home computer or even your doctor. :-

PSA_a x t

PSA_b - PSA_a

Where PSA_a is the first value PSA_b is the second value and t is the time between them. (E.G a PSA increases from 2 to 3 over 3 months the PSAdt = 2/1 x 3 = 6 months). The PSAdt is much more accurate and sensitive to progression and prognosis that a single value. For example, a trial published by Fowler in 1995 showed that if the PSADT was < 10 months, there is a high probability of metastatic disease.

The PCA3 score

There is a new genetic test that determines whether products of genes associated with prostate cancer are present in the urine. It is useful when the PSA level is low or there is doubt whether a rise relates to cancer or inflammation. This test is not widely available can be requested in some private clinics. Men are examined rectally to massage the prostate they then produce a urine sample which is sent for analysis. The results are presented in a series of percentages:

PCA3 Score                Probability of cancer
<5                                14%
5-19                             26%
20-34                           37%
35-49                           47%
50-100                         55%
>100                            78%