Prostate specific antigen
The Prostate specific antigen is a glycoprotein which belong to the kallikrein family and is produced by the prostate epithelial cells. The gene encoding PSA is located on the chromosome 19. The protein has a protease activity and degrades semenogelin. Semenogelin gives rise to the coagulation of the semen and is especially relevant for fertility. PSA has a molecular weight of 28.4 kDa.
Major component of the prostate specific antigen is represented by its complexes with α1—antichymotrypsin (ACT) and α2-macroglobulin (AMG); a minor component circulates as a free form of prostate specific antigen. The prostate specific antigen has relatively long half-life of which lasts approximately 22-33 hours and as a result, it may take 2 or 3 weeks for the serum PSA to return to the baseline after certain procedures such as transrectal biopsy, transurethral resection of the it, and radical prostatectomy.
Levels of this specific antigen typically increase due to benign or malignant disorders of the prostate and therefore PSA blood test used in diagnostic and monitoring of the prostate diseases.
Indications for the PSA blood testing
The PSA blood test is performed as a method to detect prostate cancer in early stages of the disease and monitor the treatment of prostate cancer.
Earlier it was recommended to perform PSA blood test for males after 50 yearly, although now due to the bias, it causes the test is done only for those who are at risk of developing it cancer, namely, black men and men with a strong family history of prostate cancer.
The value of PSA of less than 4 ng/ml is considered as normal.
Increased values of PSA
The PSA blood test isn’t enough specific for cancer as the levels of the it specific antigen appear elevated in various benign conditions such as the following:
- Benign prostatic hypertrophy;
- Urinary retention;
Some interventions or specific action may also lead to the elevation of PSA concentration in the blood including:
- Extensive exercise;
- Prostatic massage;
- Prostate needle biopsy;
- Transurethral resection of the prostate;
- Urethral instrumentation;
PSA blood test and prostate cancer
Prostate cancer is the most common malignancy in males over 70 years of age. Most prostate cancers are adenocarcinomas, other variants of prostate cancers are of epithelial and nonepithelial origin.
The PSA blood test is performed as a screening test for prostate cancer, although its accuracy remains controversial. The increased serum levels of PSA do not necessarily indicate the presence of cancer, whereas this cancer may occur even when the PSA levels appear to be in normal values. Approximately 25% of men with PSA levels between 2 and 4 µg/L may have cancer. However, the routine blood test is still very helpful to detect prostate cancer in the preclinical stage when the person doesn’t have any symptoms and doesn’t suspect the possibility of the disease.
Men with cancer have less free PSA (10% to 30%) and more PSA bound to protease inhibitors (70% to 90%) compared with men who do not have cancer.
PSA levels are proportional to the survival time, increase as the cancer progresses, decrease during the remission, and remain constant in stable disease and respectively the PSA blood test is used to monitor the course of cancer treatment.