Free PSA Reagent – Jaj International

The ARCHITECT Free PSA assay is a Chemiluminescent Microparticle Immunoassay (CMIA) for the quantitative determination of free prostate specific antigen (PSA) in human serum. The ARCHITECT Free PSA assay is intended to be used in conjunction with the ARCHITECT Total PSA assay in men aged 50 years or older with total PSA values between 4 and 10 ng/mL and DRE non-suspicious for cancer to determine the % free PSA value. The ARCHITECT
% free PSA value can be used as an aid in discriminating between prostate cancer and benign disease.

Prostate specific antigen (PSA), a member of the human kallikrein gene family, is a serine protease with chymotrypsin-like activity. The mature form of PSA is a single chain glycoprotein of 237 amino acids containing 7-8% carbohydrate as a single N-linked oligosaccharide side chain. PSA has a molecular weight of approximately 30,000 daltons. The major site of PSA production is the glandular epithelium of the prostate. PSA produced by the prostate is secreted into the seminal fluid in high concentrations. PSA is also present in urine and serum.

The function of PSA is the proteolytic cleavage of gel
forming proteins in the seminal fluid resulting in liquification of the seminal gel and increased sperm mobility. Low levels of PSA are found in the blood as a result of leakage of PSA from the prostate gland. Increasing levels of PSA are associated with prostatic pathology; including prostatitis, benign prostatic hyperplasia (BPH), and cancer of the prostate. PSA occurs in three major forms in blood.

The major immunodetectable form is PSA complexed with the serine protease inhibitor, alpha-1-antichymotrypsin (PSA-ACT). Uncomplexed, or free PSA, is the other immunodetectable form of PSA in serum. The majority of free PSA in serum appears to be an inactive form that cannot complex with protease inhibitors and may be either a PSA zymogen or an enzymatically-inactive, cleaved form of PSA.

A third form of PSA, a complex with alpha-2-macroglobulin (AMG), is not detectable with current immunoassays for PSA due to the engulfment and subsequent masking of PSA epitopes by the alpha-2-macroglobulin molecule. Immunoassays have been designed to detect free PSA, PSAACT complex, and total PSA (immunodetectable forms: e.g., free PSA and PSA-ACT).

Using these types of assays, the proportion of free PSA in the serum was found to be significantly higher in patients with BPH than in patients with prostate cancer (p < 0.00001).The proportion, or percent, of free PSA  determined by comparing the concentration of free PSA to the concentration of total PSA has been proposed as a way to improve the discrimination between BPH and prostate cancer, especially in those men with intermediate levels of total serum PSA

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