Prostate Cancer Psa Test
The prostate specific antigen (PSA) test is the most widely used test for detecting prostate cancer today, even though its result is not necessarily cancer specific. The PSA itself is an enzyme or protein that is made by the prostate gland and secreted into the blood, although small quantities of it are also made by a number of other organs or glands in the body. There is a constant level that is expected to be in the body in the instance that the patient is in perfect prostate health, but once this cancer is present, the level of the protein rises sharply over the 4.0ng/ml mark, thereby raising suspicion.
To do the test, a small sample of blood is taken from a vein in the arm and tested for the presence of PSA. The test is done in a lab and the results return with a number, which is what the doctors seek. The equipment used to test prostate specific antigen is a spectrum analyzer, which differs from manufacturer to manufacturer; a fact that may cause the results to vary somewhat as well, although there is a Stanford Protocol agreed upon by all manufacturers a while back by which they will calibrate their equipment to produce comparable results.
The PSA test assay is solid-phase, two site, monoclonal antibody immunoradiometric. The PSA in serum binds to a unique monoclonal antibody fixed on a plastic bead. Simultaneously, a separate distinct epitope of the PSA molecule is detected with a second radiolabelled monoclonal antibody. Six calibrators are used in this test at different concentrations covering the range of the test. Radioactivity is quantitated using a gamma ray counter and concentration is calculated from a standard reference curve using a plot of total counts per minute versus the log of the dose (ng/ml), connecting a straight line between each of the calibrator points.
With laboratories generally guaranteeing accuracy of no more than 80% it is understandably difficult to measure accurately in nanograms without reasonable error. However, accuracy is critical if the test is to be relied upon in spite of the even more pertinent reason for systematic errors – being instruments that have not been properly calibrated, or delayed tests in which the samples extracted are hardly valid anymore, or well – human errors.
Again it should be categorically stated that most prostate disorders lead to a spike in the PSA levels in the body; in addition, certain rare forms of prostate cancer may not even result in raised PSA levels. As a result, the test is only an indicator and a prostate biopsy is more often than not required to confirm the diagnosis.
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