What Level of CA 125 Indicates Cancer?

CA 125 is a kind of protein, spikes in the levels of which may indicate ovarian cancer. The normal range for CA 125 is 0 to 35 units/ml, but increases may indicate conditions other than cancer, and thus this test must be done in conjunction with other diagnostic tools to confirm the presence of cancer.

CA 125 is a glycoprotein (a sugar-associated protein) found in the blood that is considered a biomarker (or “tumor marker”) because it is found in greater concentrations in ovarian cancer cells. 

What Is CA 125 Measurement Used to Diagnose? 

CA 125 is commonly used:

• To help diagnose ovarian cancer in women at risk
• To detect recurrent ovarian cancer in women who have been previously treated
• To help predict treatment outcome in women with ovarian cancer and closely related cancers, such as fallopian tube and primary peritoneal cancers
• To monitor or assess treatment effectiveness
• To screen for ovarian, primary peritoneal, and fallopian tube cancers in high-risk women or in women with abnormal findings on examination or ultrasound
• Used as a marker to help determine the risk of a malignancy preoperatively

Limits of the CA 125 test include: 

• CA 125 is only elevated in about half of women who have early-stage ovarian cancer and 85% of women with advanced ovarian cancer
• This means a woman may have ovarian cancer and her levels of CA 125 may not be elevated
• Levels of CA 125 do not correlate with how much disease a person has 
• Many noncancerous conditions can also increase CA 125 levels, such as 
  • Diverticulitis
  • Endometriosis
  • Liver cirrhosis
  • Pregnancy
  • Uterine fibroids
• The National Cancer Institute and the United States Preventive Services Task Force do not recommend use of CA 125 measurements to screen women who have a low risk for developing ovarian cancer 

The normal range for CA 125 is 0 to 35 units/ml.

If you have not been diagnosed with ovarian cancer, high levels will require further testing to make a diagnosis. 

If you have been treated for ovarian cancer, and CA 125 levels are high, it may mean the cancer has returned.