Cancer antigen 125 (CA-125)

What it measures

CA-125 is a glycoprotein expressed by coelomic epithelium, including the ovary. It helps assess pelvic masses (with ultrasound in the RMI score) and monitors epithelial ovarian cancer.

Specimen and preparation

• Specimen: Serum or lithium-heparin plasma
• Tube: Gold top
• Preparation: Avoid testing during menstruation if possible.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Epithelial ovarian cancer
• Endometriosis and fibroids
• Menstruation and pregnancy
• Pelvic inflammatory disease
• Ascites, pleural effusion, liver cirrhosis
• Other cancers (endometrium, pancreas, lung)

Method

Chemiluminescent immunoassay

Good to know

Not recommended for screening the general population; many benign conditions raise it, especially before menopause.

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