CA-125, is an abbreviation for cancer antigen 125. CA-125 is a tumour marker; it is a glycoprotein as high molecular weight entity (Mr > 200,000).

It is best known as a marker for ovarian cancer, but it may also be elevated in other malignant cancers, including those originating in the endometrium, fallopian tubes, lungs, breast and gastrointestinal tract. CA-125 may also be elevated in a number of relatively benign conditions, such as endometriosis, several diseases of the ovary, and pregnancy. It also tends to be elevated in the presence of any inflammatory condition in the abdominal area, both cancerous and benign. Thus, CA-125 is not perfectly specific for cancer nor is it perfectly sensitive since not every patient with cancer will have elevated levels of CA-125 in the blood. CA-125 is clinically approved for following the response to treatment and predicting prognosis after treatment. It is especially useful for detecting the recurrence of ovarian cancer. Its potential role for the early detection of ovarian cancer is controversial and has not yet been adopted for widespread screening efforts in asymptomatic women.

Elevated levels in post-menopausal women are usually an indication that further screening is necessary. In pre-menopausal women, the test is less reliable as values are often elevated due to a number of non-cancerous causes.

May be diagnosed by:

• Determination of specific antibodies based on the ELISA technique
• Determination of specific antibodies based on the RIA-technique

CA 125 ELISA:

Immunoenzymatic colorimetric method for quantitative determination of CA 125 in human serum.

Principle of the Assay:

In this method, CA-125 calibrators, patient specimens and/or controls containing the native antigen are first added to streptavidin coated wells. Biotinylated monoclonal and horseradish peroxidase (HRP) labeled antibodies are added and the reactants are mixed. The different types of antibodies used have high affinity and specificity and are directed against distinct and different epitopes of CA- 125. Reaction between the various CA-125 antibodies and native CA-125 occurs in the microwells without competition or sterics hindrance forming a soluble sandwich complex. 

The interaction is illustrated by the following equation:

 
BtnAb(m) = Byotinilated Monoclonal Antibody (Excess Quantity)
AgCA-125 = Native Antigen (Variable Quantity)
E-Ab = enzyme labeled Antibody (Excess Quantity)
HRP-Ab(p)-AgCA-125-BtnAb(m) = Antigen-Antibodies Sandwich Complex  
Ka = Rate Constant of Association
K-a = Rate Constant of Dissociation

Simultaneously, the complex is fixed to the well through the high affinity reaction of streptavidin and biotinylated antibody. This interaction is illustrated below: 

Streptavidin CW = Streptavidin immobolized on well.
Immobilized Complex = Antibodies-Antigen sandwich bound.

After equilibrium is attained, the antibody-bound fraction is separated from unbound antigen by aspiration. The native antigen concentration is directly proportional to the HRP activity in the antibody-bound fraction. The activity of the conjugated HRP is quantitated by reaction with TMB substrate to produce blue colour. The reaction is terminated by adding stop solution which turns the blue colour into yellow. The absorbance is measured on a plate reader.

Specific performance characteristics: 

Correlation with RIA performed on 121 samples is r = 0.98

Order information: