A CA-125 blood test is used to detect a particular protein in the blood. While the test isn't accurate in all women, it is used to look for early cancers in certain high-risk patients and to monitor a patient's response to cancer treatment, according to Mayo Clinic.
Types of cancers that can cause elevated CA-125 levels include ovarian cancer, pancreatic cancer and stomach cancer. Noncancerous medical conditions can also cause elevated CA-125 levels, including endometriosis, pancreatitis and lupus, according to WebMD.
Doctors use it to screen for ovarian cancer in women who are at high risk of ovarian cancer, such as women who have a strong family history of ovarian cancer or women with a BRCA1 or BRCA2 gene mutation. Doctors may combine the CA 125 blood test may with transvaginal ultrasound to screen these women at six-month intervals.
When used alone, a CA-125 test is not as accurate in detecting early-stage ovarian cancer, as it only returns a positive result in 50 percent of cases, according to Johns Hopkins. However, for stage II, stage III and stage IV cancer patients, there is an 80 percent chance of the test returning a positive result.