Prostate-specific Antigen ELISA - Free PSA

Enzyme Immunoassay for the Quantitative Determination of Free Prostate Specific Antigen (f-PSA) in Serum

FOR RESEARCH USE ONLY. NOT FOR USE IN DIAGNOSTIC PROCEDURES

SUMMARY
Prostate-specific antigen (PSA), also known as gamma-seminoprotein or kallikrein-3 (KLK3), is a glycoprotein enzyme encoded in humans by the KLK3 gene. PSA is a member of the kallikrein-related peptidase family and is secreted by the epithelial cells of the prostate gland. PSA is produced for the ejaculate, where it liquefies semen in the seminal coagulum and allows sperm to swim freely. It is also believed to be instrumental in dissolving cervical mucus, allowing the entry of sperm into the uterus. PSA is present in small quantities in the serum of men with healthy prostates, but is often elevated in the presence of prostate cancer or other prostate disorders. The United States Preventive Services Task Force (USPSTF, 2012) does not recommend PSA screening, noting that the test may result in “overdiagnosis” and “overtreatment” because "most prostate cancer is asymptomatic for life," and treatments involve risks of complications including impotence (erectile dysfunction) and incontinence. The USPSTF concludes "the potential benefit does not outweigh the expected harms." PSA is not a unique indicator of prostate cancer, but may also detect prostatitis or benign prostatic hyperplasia. 30 percent of patients with high PSA have prostate cancer diagnosed after biopsy.

PRINCIPLE OF THE TEST
The f-PSA ELISA test is a solid phase two-site immunoassay. An anti-f-PSA monoclonal antibody is coated on the surface of the microtiter wells and a goat anti-PSA antibody labeled with horseradish peroxidase is used as the tracer. The f-PSA molecules present in the standard solution or sera are "sandwiched" between the two antibodies. Following the formation of the coated antibody-antigen- antibody-enzyme complex, the unbound antibody-enzyme tracers are removed by washing. The horseradish peroxidase activity bound in the wells is then assayed by a colorimetric reaction. The intensity of the color formed is proportional to the concentration of f-PSA present in the sample.

EXAMPLE OF STANDARD CURVE
Results of a typical standard run with optical density readings at 450 nm shown in the Y axis against Prostate-specific antigen concentrations shown in the X axis. This standard curve is for the purpose of illustration only, and should not be used to calculate unknowns. Each user should obtain his or her own data and standard curve.