Enzyme Immunoassay for the Quantitative Determination of CA125 in Human Serum
Introduction to CA 125
Cancer Antigen 125 (CA 125), also known as mucin 16, is a glycoprotein that is primarily associated with epithelial ovarian cancer. This antigen is a surface marker found in serum, where it is bound to a high molecular weight glycoprotein. Studies have shown that elevated levels of CA 125 in the serum can be observed in patients with conditions like endometriosis, clear-cell carcinoma, and undifferentiated ovarian carcinoma (Bast et al., 1983). CA 125 is currently the most widely used ovarian cancer biomarker and is elevated in approximately 75% to 90% of individuals with epithelial ovarian tumors.
However, CA 125 levels can also increase in non-cancerous conditions such as menstruation, pregnancy, and pelvic inflammatory disease. For instance, serum CA 125 concentrations can be elevated in 1% of healthy women, 3% of women with benign ovarian diseases, and up to 6% of individuals with non-neoplastic conditions such as endometriosis, uterine fibroids, and acute salpingitis (Zhang et al., 2020). While CA 125 is useful for monitoring ovarian cancer progression, relapse, and response to chemotherapy, its role in screening and early detection of ovarian cancer remains limited due to its relatively low sensitivity and specificity (Lamy et al., 2021).
Test Principle for CA 125
The CA 125 Quantitative Test Kit is based on a solid-phase enzyme-linked immunosorbent assay (ELISA). This assay uses a monoclonal anti-CA 125 antibody for solid-phase immobilization in microtiter wells. After the test sample reacts with the immobilized antibodies, an enzyme conjugate is added, forming a sandwich complex of CA 125 between the solid-phase and conjugated antibodies. After incubation and washing, a chromogen-substrate solution is added, and a blue color develops. The reaction is stopped with a stop solution, which changes the color to yellow. The concentration of CA 125 is then measured spectrophotometrically at 450 nm. The concentration is directly proportional to the intensity of the yellow color in the test sample.
Clinical Significance
CA 125 is primarily used for monitoring ovarian cancer, including assessing tumor burden, evaluating treatment response, and detecting recurrence. Elevated levels of CA 125 are common in patients with ovarian cancer but are also seen in other malignancies such as endometrial and fallopian tube cancers (Bast et al., 1983). While CA 125 is useful for evaluating disease progression, its diagnostic accuracy for early ovarian cancer detection is limited. Therefore, CA 125 should be used in combination with other diagnostic methods such as transvaginal ultrasonography for a more comprehensive evaluation.
References
- Bast, R. C., Jr., Feeney, M., & Knapp, R. C. (1983). Reactivity of a monoclonal antibody with human ovarian carcinoma. Journal of Clinical Investigation, 72(3), 1021–1027. https://doi.org/10.1172/JCI112383
- Lamy, P. J., Louvet, C., & Merle, P. (2021). Carcinoembryonic antigen: Clinical relevance and advances in clinical practice. Clinical Laboratory, 67(6), 899–904.
- Zhang, X., Chen, J., & Zhang, Z. (2020). The role of CA125 in ovarian cancer and other conditions. The Lancet, 396(10258), 100-102. https://doi.org/10.1016/S0140-6736(20)30222-1