Dr. William Aiken, Contributor
Prostate specific antigen (PSA) is an enzyme secreted from the glandular cells of the prostate. It is a normal constituent of the prostatic component of semen and is responsible for its liquefaction or fluidity which is important in ensuring fertility.
A small quantity of PSA normally leaks across the membranes which interface between the glands of the prostate and the blood stream, thereby allowing some PSA to gain access to the blood which accounts for its presence there. The overall generic level of PSA that is acceptable in the bloodstream is 0-4ng/ml (nanograms per millilitre).
Generally, levels above this are considered abnormal and may arise from a number of conditions, cancer being only one of them, albeit the most important one. Elevated levels of PSA in the bloodstream are, therefore, not specific or diagnostic of prostate cancer. Other conditions, some of which are much more frequent than prostate cancer, often cause an elevated PSA. These include prostatitis which literally means an inflammation of the prostate gland and benign prostatic hyperplasia (BPH) which essentially is non-cancerous enlargement of the prostate.
Bicycle riding affects PSA
Everyday activities such as intercourse accompanied by ejaculation and bicycle riding can result in an elevation of the PSA. Disorders such as urinary tract infection and acute urinary retention (stoppage of water) can cause significant elevations of the PSA. Medical interventions such as passing a catheter, doing a cystoscopy (looking inside the bladder), doing a prostate biopsy or prostatic massage can all significantly elevate the PSA. A normal prostate assessment done by digital rectal examination (DRE) does not, however, elevate PSA blood levels.
A biopsy, in which tissue is sampled from the living body and then subjected to a chemical process called 'fixing' and examined by a pathologist under the microscope, is the standard way of diagnosing cancer. A prostate biopsy is not without risk, however, and urologists generally are selective in whom a biopsy is taken from to minimise the exposure of the patient to unnecessary risk, in keeping with a fundamental medical tenet: "first, do no harm".
As there can be significant overlap in the PSA readings, especially in the range of PSA between 4-10ng/ml caused by various conditions, it is not always easy to decide who should have a biopsy. Twenty five per cent of men with a PSA between 4 and 10ng/ml will be found to have prostate cancer. This means that 75 per cent of these men will not have cancer. Would it be considered good medical practice to biopsy all of these men? The answer is an emphatic 'no'. A great deal of clinical judgement, experience and knowledge of the nuances of interpreting PSA with respect to rates of PSA rising over time and the high background incidence of prostatitis in our population is required when making decisions regarding prostate biopsy.
Age and speed
Some derivatives of PSA help us in making those tough decisions whether to recommend biopsy. These include PSA velocity, free to total PSA ratios, age specific PSA and PSA density. In many instances, prostatitis causes an elevation in the PSA between 4 and 10ng/ml without causing any symptoms whatsoever. In cases where this is suspected, empiric treatment with an anti-inflammatory and an antibiotic for six weeks followed by a repeat PSA test is perfectly acceptable.
If the PSA declines to within normal levels, a biopsy will not be necessary. If it remains elevated then an ultrasound-guided biopsy should be performed as there would be a strong clinical suspicion of cancer in this scenario. Based on the above, it should be appreciated that the decision to do a prostate biopsy is not always easy and does not simply involve a biopsy 'trigger' above 4ng/ml.
Dr. William Aiken is the head of Urology at the University Hospital of the West Indies and immediate past president of the Jamaica Urological Society; email: yourhealth@gleanerjm.com.
