What Are Normal PSA Levels?

PSA is short for Prostate Specific Antigen. It is a single-chain polypeptide containing 237 amino acids. It belongs to the serine protease family with tissue-specific chymotrypsin-like action. It can decompose the major gelatinous proteins in the semen and dilute the semen. PSA is synthesized in both normal and cancer-like epithelial cells. Initially secreted into the prostate gland duct is an inactive zymogen (proPSA), which cleavages 7 amino acids at the amino terminus to form an active prostate-specific antigen. Most of the prostate-specific antigens that enter the blood circulation quickly bind to proteolytic enzyme inhibitors, mainly binding to -1 antichymotrypsin (ACT) and -2 macroglobulin (MG), and some are inactivated by proteolytic enzymes. Exist in a free state. PSA is tissue-specific and only exists in human prostate acinar and ductal epithelial cell cytoplasm, and is not expressed in other cells. But it is not tumor-specific, and prostatitis, benign prostatic hyperplasia, and prostate cancer can all lead to an increase in total PSA levels (free PSA plus PSA).

Prostate specific antigen (PSA) is a prostate-associated antigen. PSA is a single-chain glycoprotein with a molecular weight of 32kD. It is secreted by prostate epithelial cells. It is a serine protease similar to chymotrypsin. Under normal circumstances, PSA is secreted into semen, which plays a physiological role in the division of seminal vesicles and the liquefaction of semen. Normally, only very low levels of PSA are present in the blood, and an increase in PSA concentration in the serum indicates a pathological change or trauma to the prostate. PSA levels are elevated in the vast majority of patients with prostate cancer.

Prostate cancer accounts for 10% to 20% of all types of cancer in men. It is the most common cancer in men. Progress is slow. In men over 65 years of age, the incidence of prostate cancer has skyrocketed. Therefore, prostate cancer is the main cancer that threatens the lives of men over 50 It is the second leading cause of male mortality in the West. Epidemiological investigations show that with the improvement of living standards in our country, the westernization of pollution and dietary structure, the incidence of prostate cancer is also increasing, and it must be paid great attention to clinically. The BSA test is widely used to diagnose prostate cancer and is a good tumor marker. The FDA has approved the PSA test as an index for men over 50 years of age. PSA testing combined with finger rectal examination can improve the detection rate of prostate cancer. Recent studies have shown that when FSA measurements are performed with digital rectal examinations, PSA outperforms digital rectal examinations in the early diagnosis of prostate cancer. Normal males have PSA values below 4ng / ml.

PSA has an immune-specific response to prostate tissue. PSA occurs not only in normal, benign hyperplasia, or malignant prostate tissues, but also in metastatic prostate cancer, prostate fluid, and semen. However, PSA does not occur in other normal men's tissues, as well as breast, lung, colon, rectal, gastric, pancreatic, and thyroid cancers. Moreover, PSA is completely different in function and immunology from prostate acid phosphatase (PAP) ^[1]

Prostate-specific antigen (PSA) is a serine protease with chymotrypsin-like activity and belongs to the kallikrein gene family. Mature PSA is a single-chain glycoprotein consisting of 237 amino acids with a molecular weight of 3000. PSA is mainly produced by front-lined glandular epithelial cells and secreted into semen. The main function of PSA is to decompose the gelatinous protein in semen, liquefy the gelatinous semen, and enhance the mobility of sperm. A small amount of PSA can leak into the blood from the prostate. However, the increase of PSA in serum is found in the pathological state of the prostate, such as prostatitis, benign prostatic hyperplasia, and prostate. There are three main forms of PSA in the blood, two of which can be determined immunologically, namely bound PSA and free PSA. The conjugated PSA binds to a serine egg autoenzyme inhibitor (a ₁ -chymotrypsin). The detected PSA is mainly free PSA of this type, which is mostly inactive in serum and cannot be combined with serine protein inhibitors. They Either in its original form or in its broken form. The third form is a PSA that binds to a ₂ -macroglobulin. This PSA cannot be determined immunologically because the macroglobulin covers the epitope of the PSA. Prostate cancer lacks early symptoms and is not easy to diagnose. The traditional test method is digital rectal examination (DRE), but sometimes it cannot find small tumors confined to the prostate. Cooner et al. (1990) published research results on the diagnosis of early prostate cancer using prostate ultrasound examination and detection of PSA in serum, and found that abnormalities in DRE and PSA can significantly improve the predictability of prostate. Therefore, the combined test of DRE and PSA can improve the diagnosis rate of early prostate cancer. The detection of PSA in serum is not only another valuable diagnostic method of prostate except ultrasound and digital rectal examination, but also the most accurate test among the three. This test is easily accepted by patients, and its results are quantitative, objective, and independent of operator technology. For prostate cancer patients who have undergone surgery or other treatments, testing PSA is also very meaningful for detecting metastasis and recurrence. After the treatment, if the patient has a persistently elevated or re-elevated PSA, it may indicate that the swollen remains or relapses. The increase in serum PSA concentration cannot be directly used as clear evidence of prostate cancer. Prostate pathological biopsy is the basis for the diagnosis of prostate. Other factors can affect the level of PSA in the serum, such as the presence of heterosexual antibodies in the patient's serum, which occasionally increases PSA. Prostate massage, ultrasound, and biopsy of the prostate can cause a significant increase in PSA levels, so blood should be collected before prostate examinations. PSA increases after ejaculation. Hormone therapy may affect PSA expression, reduce PSA, and may obscure signs of disease recurrence ^[2]

1. Serum PSA is a specific marker of prostate cancer: it is of great significance for the diagnosis of early asymptomatic prostate cancer. Normally, PSA is produced by prostate epithelial cells.

In addition to the known prostate-related marker PSA, there is also prostate acid phosphatase (PAP), an enzyme secreted by the prostate. PAP rarely enters the blood when it is normal. In prostate cancer, malignant cells produce PAP and enter the blood. The normal value of serum PAP is less than 3.5ng / ml. It is believed that PAP has a limited effect, but is considered to be another independent predictor of treatment failure after radical prostatectomy, although it cannot predict the stage and surrounding organs. Prostate specific peptide (PSP) and Prostate specific membrane antigen (PSMA), because the expression of PSMA in prostate cancer epithelial cells is not affected by the degree of tumor cell differentiation, and it remains after castration It has higher expression, and it is more meaningful to detect PSP and PSMA than PSA or PAP. This indicator has certain clinical value for the early diagnosis, recurrence and progression of prostate cancer.