PSA (prostate-specific antigen) free

PSA is a specific protein that is produced in the prostate gland and is used to diagnose oncological and inflammatory diseases of the prostate. PSA is synthesized by the cells of the excretory ducts of the prostate gland and is necessary for dilution of the ejaculate. Outside the prostate, the site of PSA production is the paraurethral glands and the breast.

The prostate-specific antigen enters the bloodstream in small amounts and is detected in the form of three fractions:

• Free;
• Bound to alpha-1-antichymotrypsin;
• Bound to alpha-2-macroglobulin.

It is extremely difficult to determine the bound fraction by publicly available laboratory means, since PSA is located "inside" these chemical complexes. For this reason, only PSA-General and PSA-free are defined. These two tests together are of great diagnostic value. Knowing the level of both fractions, it is possible to calculate the free PSA index using the formula:

In prostate cancer, PSA is mainly in a bound state, therefore, the percentage of free testosterone will be lower. The Free PSA index is the probability of cancer:

• 0-10%: 56%;
• 10-15%: 28%;
• 15-20%: 20%;
• 20-25%: 16%;
• more than 25%: 8%.

Attention! It is recommended to take two tests at the same time: general PSA and free PSA. The test is done no earlier than 7 days after prostate massage, transrectal ultrasound or finger rectal analysis, as a false positive result is possible. Read also: "Prostate-specific antigen and men's health", "Men's health: myths and reality", profile "Men's health".