PSA is a protein molecule made by prostate gland cells. Its function is to liquefy the stored seminal coagulum and thus enhance the motility of the sperm cells to aid fertilization. The protein also prevents sperm cells clumping together. PSA stands for prostatic specific antigen. This does not mean it is an antigen in the sense that it can attack you. It refers to the fact that an antibody was developed that could recognise it and attach to it. For all intents and purposes PSA is made only by the prostate gland hence the word specific. However it is known that really tint quantities in the blood do originate in other glands of the body.
Very small amounts of the PSA protein leak out of the gland into the blood stream from the prostate gland cells that make the PSA. Therefore all men will have detectable levels of PSA in their bloodstreams unless they have a congenital absence of the prostate gland or the gland has been removed.
There is a so-called normal level of PSA in the blood. It should be less than four nanograms per millilitre. However this time honoured value really is fairly meaningless and one should not believe that there is a cancer present if the PSA is higher than 4 ng/ml nor should one feel a cancer cannot be present if the PSA is less than 4 ng/ml. in the USA, the trend has moved to investigating men with a PSA of over 2,6 ng/ml.
PSA comes in different varieties. The two commonest forms of PSA are called free PSA and complexed PSA. Free PSA floats around in the blood stream on its own whilst complexed PSA is bound to a protein carrier molecule in the blood. The total PSA is the sum of these two types of PSA. The less common varieties of PSA can be ignored in the total because they contribute less than 1% of the total sum. There is a so called normal ratio of free PSA and complexed PSA such that there should be 1 part free PSA to 3 parts complexed PSA or free PSA should be around 25% of the total.
If the ratio of free to complexed PSA changes in that there is relatively more complexed PSA or less free PSA making up the total then this could indicate that a tumour is present. Early cancers resemble normal cells very closely. Also they function in most respects like a normal cell and as such these cells make PSA as well. A major difference between a normal cell and a cancer cell is that cancer cell walls tend to be more leaky and PSA, particularly complexed PSA, is lost more readily into the blood stream. This explains why the PSA can rise when a cancer is present and also why the complexed PSA can increase in relation to the free PSA when a cancer is present.
Prostate glands in the majority of men tend to enlarge as men age. This is because there are new prostate cells being made all the time but very few if any are dieing. Because there are more cells making PSA, this means that the level of PSA will gradually rise in men as they grow older. There is therefore a concept known as age related PSA value. The urologist will take this into account when he assesses you for a possible cancer. A man of 70 years can have a PSA of 6 and be comfortable with this level however a man of 40 years should have a PSA of less than 2,5 ng/ml.
Because of the gradual increase in size of the prostate gland, PSA will therefore rise slightly on an annual basis. This annual rate of rise is called PSA velocity. PSA velocity is concept that is no longer in vogue. It used to be said that the PSA should not rise by more than 0,75 ng/ml/year. Experience with PSA has shown this concept to be of little use in monitoring for cancer development. However when a cancer is suspected; and there is a persistent and significant increase in the PSA, then the patient and the urologist will need to be more vigilant in searching for a developing cancer.
Another tool is to check the PSA doubling time. This is the time taken for the PSA level to double. A doubling time of several years is much less worrying than one of several months.
Cancer is not the only cause of a raised PSA. As mentioned previously prostate size affects the gland. Benign enlargement or BPH, of the prostate gland is a very common condition of the ageing male. It is far more common than cancer in terms of its clinical impact. Only around 10% of men will develop a clinical prostate cancer in their life times yet at least forty percent of men will suffer from symptoms related to a prostate causing obstruction to the bladder. BPH does not turn into a cancer. This is a common belief among the public and even some medical practitioners.
Secondly inflammation of the prostate gland called prostatitis will cause the PSA to rise. Acute inflammation can cause the PSA to rise several fold. Even following treatment the PSA may take several weeks to return to a baseline level. Chronic inflammation is a common condition that may or may not produce symptoms. It can cause the PSA to increase as well but usually the increase is small but persistent. It is important to treat prostatitis before making any judgement call on the PSA level. It should be noted that prostatitis can be very difficult to treat because antibiotics find it very difficult to penetrate the prostate gland. Furthermore there are other more common conditions of prostatitis than bacterial infection and in these cases antibiotics will have no affect anyway.
Several factors can affect the PSA level that have nothing to do with disease. These factors are important to note before you have a PSA test.
Firstly the laboratory used should always be the same. Different labs use different techniques to measure PSA and thus there can be significant differences in the results of the same blood tested by different labs. Furthermore the lab conditions vary from day to day and it would be unusual for any one lab to be able to meet a consistency of greater than 80% in their testing methods.
PSA should be taken prior to any digital rectal examination. However this is not always practical. The doctor who exams you, if diligent will include a digital rectal examination in his repertoire of clinical tests. The presence of an abnormality will then direct him or her to ask for a PSA test. The rectal exam can raise the PSA by 10%. This can be taken into account by the examining doctor but for patients who have a deep seated interest in monitoring their PSA accurately this can be irritating and possibly lead to unnecessary worry. The wisest course is to ask for a PSA test before any rectal examination.
The prostate gland lies very close to the perineal area. This is the part of your body that is in contact with a saddle on a bicycle or motor bike or a horse. The jarring of the saddle against the perineal region can cause the PSA to rise. Therefore before a PSA test these activities should not be undertaken for about a week.
Sexual intercourse can also cause the PSA to rise for up to two days. On should thus be celibate for two days prior to the test.
Alcohol and coffee may have an affect on PSA and so these beverages should be avoided prior to the PSA test. Lastly never accept the so called normal PSA level as meaning you cannot have a cancer. Beware the doctor who will base the presence or absence of a cancer purely on a PSA result. That is bad medical practise.