PSA ELISA Kit

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96 Tests Kit

Enzyme Immunoassay for the Quantitative Determination of PSA Concentration in Human Serum

Prostate-Specific Antigen (PSA): Biological Role and Diagnostic Significance

Prostate-Specific Antigen (PSA) is a single-chain glycoprotein belonging to the kallikrein family of serine proteases, with enzymatic activity similar to chymotrypsin (Lilja et al., 2008). The PSA monomer, with a molecular weight of approximately 30 kDa, is produced by prostate epithelial cells and is primarily secreted into seminal fluid. Its primary physiological function is to facilitate gel dissolution in freshly ejaculated semen by proteolysis of major gel-forming proteins (Stenman et al., 1999).

In circulation, the majority (70–90%) of PSA is complexed with alpha-1-antichymotrypsin (ACT), forming a high-molecular-weight complex of approximately 90–100 kDa (Lilja et al., 2008). Total PSA, which includes both free PSA and PSA-ACT complex, is elevated in both benign prostatic hyperplasia (BPH) and malignant prostate cancer. The ratio of free to complexed PSA varies among individuals and is an important diagnostic marker. While PSA is present at low detectable levels in the blood of healthy individuals, an increase in PSA concentration is a significant indicator of both benign and malignant prostate tumors (Catalona et al., 1994).

PSA testing is a reliable diagnostic tool for prostate cancer detection and for monitoring patients after treatment or surgery (Thompson et al., 2004). Prostate cancer is the second most prevalent cancer in developed countries and has a high mortality rate. However, since PSA levels can also increase due to benign prostate conditions such as BPH, PSA testing alone is not a confirmatory test for prostate cancer. Instead, PSA testing is most valuable when used in combination with other diagnostic assessments such as digital rectal examination (DRE), imaging techniques, and biopsy (Stenman et al., 1999). Following radical prostatectomy, PSA levels should become undetectable; levels exceeding 0.1 ng/mL post-surgery may indicate residual prostate tissue or metastasis (Heidenreich et al., 2014).

Test Principle

The PSA Quantitative Test Kit is based on a solid-phase enzyme-linked immunosorbent assay (ELISA). This assay employs an anti-PSA antibody immobilized onto a microtiter plate as the solid phase, along with a mouse monoclonal anti-PSA antibody conjugated to horseradish peroxidase (HRP) as the detection antibody.

During the assay procedure, the test sample is incubated with the immobilized anti-PSA antibody. After washing, the enzyme-conjugated antibody is added, forming a sandwich complex with the PSA antigen. A chromogenic substrate is then introduced, resulting in a colorimetric reaction. The reaction is terminated by the addition of a stop solution, leading to a color change from blue to yellow, which is measured spectrophotometrically at 450 nm. The intensity of the color is directly proportional to the PSA concentration in the sample (Engvall, 1980).

Clinical Significance

PSA measurement plays a crucial role in various clinical contexts, including:

  1. Prostate Cancer Detection: PSA is a key biomarker in detecting prostate cancer. Elevated PSA levels in blood can indicate the presence of prostate cancer, especially when combined with other diagnostic methods. It is particularly useful in monitoring the progression of the disease, evaluating response to treatment, and detecting recurrence after therapy (Thompson et al., 2004).
  2. Benign Prostatic Hyperplasia (BPH): PSA is also elevated in cases of BPH, a non-cancerous enlargement of the prostate. While PSA testing alone cannot distinguish between cancerous and benign conditions, it serves as an initial screening tool that, when combined with other diagnostic tests, helps in determining the appropriate treatment strategy.
  3. Monitoring After Prostate Surgery: After prostatectomy (surgical removal of the prostate), PSA levels should decrease to undetectable levels. Any detectable PSA post-surgery may indicate the presence of residual prostate tissue or metastasis, thus providing a useful indicator for assessing the success of the surgery and guiding follow-up care (Heidenreich et al., 2014).
  4. Screening in Asymptomatic Patients: PSA testing is commonly used for early screening in asymptomatic men, especially those at higher risk for prostate cancer, such as those with a family history of the disease. Regular PSA testing, along with other clinical assessments, can help detect prostate cancer in its early stages when treatment options are more effective.
  5. Predicting Disease Recurrence: Elevated PSA levels post-treatment, such as after radiation therapy or prostatectomy, can be indicative of disease recurrence. Monitoring PSA levels over time helps clinicians detect recurrences early, enabling timely intervention and improving patient outcomes.
  6. Guiding Treatment Decisions: PSA testing is also instrumental in guiding treatment decisions for patients with prostate cancer. It is used to assess the effectiveness of treatments like chemotherapy, radiation, or hormone therapy, and helps clinicians tailor treatments to individual patient needs.

References

  • Catalona, W. J., Smith, D. S., Ratliff, T. L., Dodds, K. M., Coplen, D. E., Yuan, J. J., … & Basler, J. W. (1994). Measurement of prostate-specific antigen in serum as a screening test for prostate cancer. New England Journal of Medicine, 330(8), 1128-1134. https://doi.org/10.1056/NEJM199404283301702
  • Engvall, E. (1980). Enzyme immunoassay ELISA and EMIT. Methods in Enzymology, 70, 419-439. https://doi.org/10.1016/0076-6879(80)70041-3
  • Heidenreich, A., Bastian, P. J., Bellmunt, J., Bolla, M., Joniau, S., Van Der Kwast, T., … & Mottet, N. (2014). EAU guidelines on prostate cancer. Part 1: Screening, diagnosis, and local treatment with curative intent—update 2013. European Urology, 65(1), 124-137. https://doi.org/10.1016/j.eururo.2013.09.046
  • Lilja, H., Ulmert, D., & Vickers, A. J. (2008). Prostate-specific antigen and prostate cancer: Prediction, detection, and monitoring. Nature Reviews Cancer, 8(4), 268-278. https://doi.org/10.1038/nrc2351
  • Stenman, U. H., Hakama, M., Knekt, P., Aromaa, A., Teppo, L., & Leinonen, J. (1999). Serum concentrations of prostate-specific antigen and its complex with α1-antichymotrypsin before diagnosis of prostate cancer. The Lancet, 354(9187), 20-21. https://doi.org/10.1016/S0140-6736(99)01406-4
  • Thompson, I. M., Pauler, D. K., Goodman, P. J., Tangen, C. M., Lucia, M. S., Parnes, H. L., & Coltman, C. A. (2004). Prevalence of prostate cancer among men with a prostate-specific antigen level ≤ 4.0 ng per milliliter. New England Journal of Medicine, 350(22), 2239-2246. https://doi.org/10.1056/NEJMoa031918