Free PSA percentage
Why this test?
- For early diagnosis of prostate cancer.
- Detection of relapse and metastases after treatment.
In what cases is it prescribed?
- For monitoring the course of the disease, preclinical diagnosis of metastasis and evaluation of the effectiveness of prostate carcinoma therapy.
- To monitor the condition of patients with prostatic hypertrophy, in order to detect prostate carcinoma as early as possible.
- Screening examination of men over 50 years old, detection of PSA level dynamics.
Prostate-specific antigen is a physiological excretory product of the prostate gland. It has enzymatic (protease) activity, reducing the viscosity of semen. It is contained in the cytoplasm of epithelial cells of the prostate ducts.
PSA is found in normal prostate tissue, adenoma and prostate cancer metastases, prostatic juice and seminal plasma, but is not present in other normal or tumorous human tissues. The half-life is 4 days.
In blood serum prostate-specific antigen is found in two forms - free and bound to various antiproteases. The content of free form (f-PSA) is about 10% of the total PSA.
Most of PSA (90%) is bound to alpha 1 anti-chymotrypsin and is available for laboratory determination. A small part of the prostate antigen is bound to alpha 2-macroglobulin and is inaccessible for investigation by conventional methods, because the PSA molecule is inside the complex. The free and bound fractions make up the total PSA.
The ratio of free PSA to total PSA, expressed as a percentage, is referred to as the free PSA index. This index is calculated by the formula: PSA index = (PSA free / PSA total) *100%. In men whose PSA index is less than 15%, a prostate biopsy is recommended. If the PSA index value is more than 15%, the risk of prostate cancer is lower and a biopsy may not be necessary.