Cancer Antigen (CA) 125

Additional Information:

UFHPL Epic order code: LAB2107306

This immunoassay is intended for the in vitro quantitative determination of OC 125 reactive determinants in human serum and plasma.1 The Elecsys CA 125 II assay is indicated for use as an aid in the detection of residual or recurrent ovarian carcinoma in patients who have undergone first-line therapy and would be considered for second-look procedures.1 The Elecsys CA 125 II assay is further indicated for serial measurement of CA 125 to aid in the management of cancer patients.1 CA 125 belongs to the family of hybridoma-defined tumor markers. The values measured are defined by the use of the monoclonal antibody (MAb) OC 125. The antigenic determinant CA 125 is located on a high-molecular weight glycoprotein (200 – 1000 kd) isolated from cell culture or serum. The antigenic determination CA 125 has a protein structure with associated carbohydrate sidechains.2, 3 These determinants are associated with a high-molecular weight glycoprotein in serum and plasma of women with primary epithelial invasive ovarian cancer (excluding those with cancer of low malignant potential).

CA 125 is found in a high percentage of nonmucinous ovarian tumors of epithelial origin4 and can be detected in serum.5, 6 It does not occur on the surface epithelium of normal ovaries (adult and fetal). Ovarian carcinoma accounts for about 20 percent of gynecologic tumors; the incidence is 15/100,000.7 CA 125 has been found in the amniotic fluid and in the coelomic epithelium; both of these tissues are of fetal origin. In tissues of adult origin, the presence of CA 125 has been demonstrated in the epithelium of the oviduct, in the endometrium, and in the endocervix.8

Elevated values are sometimes found in various benign gynecologic diseases, such as ovarian cysts, ovarian metaplasia, endometriosis, uterus myomatous, or cervicitis. Slight elevations of this marker may also occur in early pregnancy and in various benign diseases (e.g., acute and chronic pancreatitis, benign gastrointestinal diseases, renal insufficiency, autoimmune diseases, and others). Markedly elevated levels have been found in benign liver diseases, such as cirrhosis and hepatitis. Extreme elevations can occur in any kind of ascites due to malignant and benign diseases. Although the highest CA 125 values occur in patients suffering from ovarian carcinoma, clearly elevated values are also observed in malignancies of the endometrium, breast, gastrointestinal tract, and various other malignancies.

Although CA 125 is a relatively unspecific marker,9 – 13 it is today the most important tumor marker for monitoring therapy and progress of patients with serous ovarian carcinoma. At primary diagnosis, the sensitivity of CA 125 depends on the FIGO stage (FIGO = Federation of Gynecology and Obstetrics); higher tumor stages are associated with higher CA 125 levels.14

The diagnostic sensitivity and specificity of the Elecsys CA 125 II test was calculated by comparing ovarian carcinoma patients at primary diagnosis (FIGO stage I to IV) with patients suffering from benign gynecologic diseases.1

At a cutoff value of 65 U/mL, the sensitivity is 79 percent (at a low specificity of 82 percent). The cutoff level has to be raised if higher specificity is desired. The optimal clinical value is reached at 150 U/mL (sensitivity 69 percent, specificity 93 percent).1


  1. CA 125 on Elecsys 1010/2010 and Modular Analytics E170, [Package insert]. 2007-08, VII, Indianapolis, Ind: Roche Diagnostics; 2007.
  2. Davis HM, Zurawski VR Jr, Bast RC Jr, Klug TL. Characterization of the CA 125 antigen associated with human epithelial ovarian carcinomas. Cancer Res. 1986 Dec; 46(12 Pt 1):6143-6148. PubMed 2430690
  3. Diamandis EP, Fritsche HA, Lilja H, et al. Tumor Markers: Physiology, Pathobiology, Technology, and Clinical Applications. 1st ed. Washington, DC: AACC Press; 2002.
  4. Kabawat SE, Bast RC, Welch WR, Knapp RC, Colvin RB. Immunopathologic characterization of a monoclonal antibody that recognizes common surface antigens of human ovarian tumors of serous, endometrioid, and clear cell types. Am J Clin Pathol. 1983 Jan; 79(1):98-104. PubMed 6336888
  5. Bast RC Jr, Klug TL, St John E, et al. A radioimmunoassay using a monoclonal antibody to monitor the course of epithelial ovarian cancer. N Engl J Med. 1983 Oct 13; 309(15):883-887. PubMed 6310399
  6. Klug TL, Bast RC Jr, Niloff JM, Knapp RC, Zurawski VR Jr. Monoclonal antibody immunoradiometric assay for an antigenic determinant (CA 125) associated with human epithelial ovarian carcinomas. Cancer Res. 1984 Mar; 44(3):1048-1053. PubMed 6198078
  7. Hasholzner U, Baumgartner L, Stieber P, Meier W, Hofmann K, Fateh-Maghadam A. Significance of the tumour markers CA 125 II, CA 72-4, CASA, and CYFRA 21-1 In ovarian carcinoma. Anticancer Res. 1994 Nov-Dec; 14(6B):2743-2746. PubMed 7532929
  8. Kabawat SE, Bast RC Jr, Bhan AK, Welch WR, Knapp RC, Colvin RB. Tissue distribution of a coelomic epithelium-related antigen recognized by the monoclonal antibody OC 125. Int J Gyn Path. 1983; 2(3):275-285. PubMed 6196309
  9. Daoud E, Bodor G. CA-125 concentrations in malignant and nonmalignant disease. Clin Chem. 1991 Nov; 37(11):1968-1974. PubMed 1934471
  10. Kenemans P, Bon GG, Kessler A, Verstraeten AA, van Kamp GJ. Multicenter technical and clinical evaluation of a fully automated enzyme immunoassay for CA 125. Clin Chem. 1992 Aug; 38(8 Pt 1):1466-1471. PubMed 1643716
  11. Hasholzner U, Stieber P, Baumgartner L, et al. Methodological and clinical evaluation of three automatized CA 125 assays compared with CA 125 II RIA (Fujirebio). Tumordiagn Ther. 1994; 15:114-117.
  12. Ruibal A, Encabo G, Martinéz-Miralles E, et al. CA 125 seric levels In nonmalignant pathologies. Bull Cancer. 1984; 71(2):145-146. PubMed 6203578
  13. Zahner J, Schmitz FJ, Schmitz G, et al. CA 125—ein tumor marker in der inneren medizin. Lab Med. 1995; 19:185-188.
  14. Stieber P, Fateh-Moghadam A. Sensible Use of Tumor Markers. Marloffstein-Rathsberg: Juergen Hartmann Verlag;1993. Boehringer Mannheim, Catalogue N° 1536869 (Engl), 1320947 (German). ISBN 3-926725-07-9 German/English.

CPT Code(s):


Specimen Requirements:

Important: Values obtained with different assay methodologies should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor a patient’s course of therapy. This procedure does not provide serial monitoring; it is intended for one-time use only.

Patient Preparation: It is recommended that this assay not be performed until at least three weeks after the completion of primary chemotherapy and at least two months following abdominal surgery.

Type: Serum

Container/Tube: Red-top tube or gel-barrier tube
  • If a red-top tube is used, transfer the separated serum to a plastic transport tube.

Sample Volume: 0.8 mL

Minimum Volume: 0.3 mL (Repeat testing is not possible with this specimen volume.)

Storage: Freeze specimens immediately after collection.

Stability (collection to time of analysis/testing):

  • Ambient: 14 days
  • Refrigerated: 14 days
  • Frozen: 14 days
Rejection Criteria:

  • Citrate plasma specimen
  • Improper labeleing


The Elecsys CA 125 II assay is labeled “For in vitro diagnostic use” in the manufacturer’s package insert.1


The measured CA 125 value of a patient’s sample can vary depending on the test procedure used. The laboratory finding must, therefore, always contain a statement on the CA 125 assay method used. CA 125 values determined on patient samples by different test procedures cannot be directly compared with one another and could cause erroneous medical interpretations.

In patients receiving therapy with high biotin doses (eg, >5 mg/day), no sample should be taken until at least eight hours after the last biotin administration.1 As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes.1 In rare cases, interference due to extremely high titers of antibody to streptavidin and ruthenium can occur. The test contains additives that minimize these effects.1

For diagnostic purposes, the results should always be assessed in conjunction with the patient’s medical history, clinical examination, and other findings.


Electrochemiluminescence immunoassay (ECLIA)

Reference Values:

0.0 – 34.0 units/mL