CA 125 Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is CA 125?

CA 125 (cancer antigen 125) is a protein found on the surface of many types of cells, but it is produced in particularly high amounts by ovarian cancer cells. It is the most widely used tumour marker for epithelial ovarian cancer, which accounts for approximately 90% of all ovarian cancers.

It is important to understand that CA 125 is not a definitive cancer test. While it is elevated in about 80% of advanced ovarian cancers, it can also be raised in many benign (non-cancerous) conditions. Conversely, it may be normal in early-stage ovarian cancer. CA 125 is most valuable when used for monitoring treatment response and detecting recurrence, rather than as a standalone screening tool.

Why Is CA 125 Tested?

• Monitor treatment response in patients with diagnosed ovarian cancer
• Detect ovarian cancer recurrence after treatment — CA 125 often rises months before symptoms or imaging findings
• Evaluate pelvic masses — helps distinguish benign from malignant ovarian cysts
• As part of the Risk of Malignancy Index (RMI) combining CA 125, ultrasound, and menopausal status
• Screen high-risk women (BRCA1/BRCA2 mutation carriers) alongside transvaginal ultrasound
• Monitor endometriosis severity in some clinical settings

Normal Ranges

Pre-menopausal women commonly have mild CA 125 elevations from menstruation, ovulation, endometriosis, or fibroids. Post-menopausal elevation is more clinically significant.

Causes of High CA 125

Malignant Causes

• Ovarian cancer: Elevated in ~80% of advanced cases and ~50% of stage I cases
• Endometrial cancer: Moderately elevated in some cases
• Fallopian tube cancer: Often produces CA 125 similarly to ovarian cancer
• Peritoneal cancer: Primary peritoneal carcinomatosis often raises CA 125
• Other cancers: Breast, lung, pancreatic, and colon cancers can occasionally elevate CA 125

Benign Causes

• Endometriosis: One of the most common non-malignant causes of elevated CA 125
• Pelvic inflammatory disease (PID): Infection raises CA 125
• Fibroids (leiomyomas): Large fibroids can moderately elevate CA 125
• Ovarian cysts: Benign functional cysts may cause mild elevation
• Menstruation: CA 125 can double during menses
• Early pregnancy: First trimester elevations are normal
• Liver disease: Cirrhosis and hepatitis can raise CA 125 significantly
• Heart failure: Pleural and peritoneal fluid accumulation raises CA 125
• Kidney disease: Peritoneal dialysis patients often have elevated CA 125

Causes of Low CA 125

Low CA 125 is not clinically concerning and does not indicate a health problem. Values near zero simply reflect low production of the protein.

CA 125 in Ovarian Cancer Screening

Current UK guidelines (NICE) do not recommend routine CA 125 screening for the general population because:

• CA 125 is not sensitive enough for early-stage disease (misses ~50% of stage I cancers)
• Many benign conditions cause false positives, leading to unnecessary anxiety and invasive testing
• The UKCTOCS trial showed CA 125 screening detected more cancers but did not significantly reduce mortality

However, testing IS recommended when:

• A woman presents with symptoms: persistent bloating, pelvic pain, early satiety, or urinary frequency
• A pelvic mass is found on examination or imaging
• A woman carries BRCA1/BRCA2 mutations or has strong family history

When Should You Get Tested?

• You have persistent abdominal bloating that doesn't resolve
• You experience pelvic or abdominal pain for more than 3 weeks
• You feel full quickly when eating or have difficulty eating
• You have unexplained urinary frequency or urgency
• You have a family history of ovarian or breast cancer
• You carry a BRCA1 or BRCA2 gene mutation
• A pelvic mass has been found and needs further investigation

Which Lola Health Tests Include CA 125?

CA 125 is available as an add-on biomarker with Lola Health tests:

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