Special remarks:

PSA (Prostate Specific Antigen) is a serine protease of the kallikrein group, found almost exclusively in the prostate. It is a glycoprotein with a molecular weight of 34.000 D, which plays a major role in the liquefaction of seminal fluid.
Two forms of PSA exist simultaneously in serum, the free form, and that complexed to anti-proteases, a1 antichymotrypsin (PSA-ACT) and a2 macroglobulin. Conventional PSA assays measure PSA and PSA-ACT (ie total PSA) without differentiating between the two forms. Whilst a very low amount of total PSA is present in the serum of men free of any pathology, high seric levels are found in cases of benign hyperplasia, of prostatitis and particularly of prostate cancer, including its early stages (stage A).
The PSA assay must be interpreted in conjunction with the results of digital rectal examination. From a threshold of 4 ng/ml, PSA assay`s sensitivity enables it to be used as soon as prostate cancer has been diagnosed and throughout the different steps of the disease: establishment of stage, tumor volume evaluation, therapeutic response especially after surgery, prognosis and during remission, for an early detection of any relapse.