The CA-125 blood test is used as a biomarker for ovarian cancer and measures the amount of the protein CA-125 in the blood. The normal range for CA-125 is 0 to 35 units/mL, and levels over 35 U/mL may indicate the presence of cancer or other conditions. However, a high level of CA-125 does not always mean that a person has cancer, as several noncancerous conditions can also cause an increase in CA-125 levels. Therefore, if a woman has not been previously diagnosed with ovarian cancer, high levels of CA-125 indicate further testing is needed to make a diagnosis. Additionally, CA-125 is only elevated in about 50% of women with early-stage ovarian cancer and 85% of women with advanced ovarian cancer, which means a woman may have ovarian cancer and levels of CA-125 may not be elevated.