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CA 125

Cancer screening Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Cancer screening

Overview

CA 125 (cancer antigen 125) is a glycoprotein produced by cells derived from coelomic and Müllerian epithelium; the blood test measures the concentration of this antigen (reported in U/mL). It is most widely used as a tumor marker for ovarian cancer—both for monitoring treatment response and detecting recurrence—but can be raised in other malignancies (endometrial, peritoneal, pancreatic, breast, lung) and many benign conditions. Symptoms that may prompt testing include new pelvic/abdominal pain or bloating, unexplained weight loss, early satiety, or a pelvic mass. Results vary with age and sex: the test is primarily used in women (especially postmenopausal), is less specific in premenopausal women because of benign causes, and is less sensitive for early-stage ovarian cancer.

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Test Preparation

Provide brief clinical history/doctor's prescription at the time of sample collection
Test should not be done immediately before or during menstruation or immediately after abdominal surgery, as these cause transiently increased levels
Pregnancy may also affect the levels of CA 125

Why Do I Need This Test

Profile: Cancer screening / tumor marker panel (commonly ordered when ovarian cancer is suspected or for monitoring known disease) - Symptoms prompting test: persistent abdominal/pelvic pain, bloating, pelvic mass, unexplained weight loss, changes in bowel/bladder habits - Conditions diagnosed/monitored: ovarian cancer (main use: monitoring and recurrence), other gynecologic or intra‑abdominal malignancies, and some benign gynecologic conditions - Reasons for abnormal levels: malignancy, benign gynecologic conditions (endometriosis, menstruation, pregnancy), pelvic inflammatory disease, liver disease, peritonitis, and non‑gynecologic cancers - Biological meaning: elevated CA 125 reflects increased expression/release of the antigen from irritated, inflamed, or malignant serosal/epithelial surfaces - Behaviors/lifestyle: recent surgery, smoking is not a direct cause; pregnancy and menstruation can raise levels transiently - Family history: strong family history of ovarian or breast cancer (especially BRCA1/2) may prompt testing and closer surveillance

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Understanding Test Results

Values ≤35 U/mL are generally considered normal.
Mild-to-moderate elevations (≈35–200 U/mL) can occur with benign conditions (menstruation, endometriosis, pelvic inflammatory disease, pregnancy, liver disease) or early/less advanced malignancy; interpretation depends on clinical context.
Levels >200 U/mL raise greater concern for ovarian or other intra‑abdominal malignancy, particularly in postmenopausal women.
Very high levels (e.g., >500–1,000 U/mL) often indicate advanced disease or extensive peritoneal involvement but are not diagnostic by themselves.
A single elevated value is not definitive—trends (rising or falling) matter more for assessing treatment response or recurrence.
Low CA 125 does not exclude early ovarian cancer (false negatives occur), so imaging and clinical assessment remain essential.

Normal Range

0-35 U/mL

FAQs

Q: What CA-125 level indicates cancer?

A: CA‑125 is a blood tumor marker; levels above about 35 U/mL are generally considered elevated. Mild rises occur with many benign conditions, while much higher values (for example >200 U/mL) more strongly suggest ovarian malignancy. CA‑125 alone does not diagnose cancer—interpretation depends on symptoms, imaging, trends over time, and menopausal status, with greater reliability in postmenopausal women.

Q: What is a CA-125 test for?

A: The CA-125 test measures the blood level of the CA‑125 protein, often used to help evaluate and monitor ovarian cancer. It can assist assessing pelvic masses, tracking treatment response, and detecting recurrence. CA‑125 is not specific—levels can rise with benign conditions (e.g., menstruation, endometriosis, infection) and other cancers—so results are interpreted with clinical findings and imaging, not used alone for general population screening.

Q: Can CA-125 detect breast cancer?

A: CA‑125 is mainly a marker for ovarian cancer and is not sensitive or specific enough to detect breast cancer. Levels can sometimes rise with breast cancer, especially in advanced disease, but CA‑125 is not recommended for breast‑cancer screening or diagnosis. Clinicians use imaging, biopsy, and other markers (e.g., CA 15‑3, CEA) for diagnosis and monitoring instead.

Q: Can CA-125 levels be high without cancer?

A: Yes. CA‑125 can be elevated for many noncancerous reasons: menstruation, pregnancy, endometriosis, uterine fibroids, pelvic inflammatory disease, benign ovarian cysts, recent surgery or inflammation, liver disease, pancreatitis, heart failure and peritonitis. It’s not specific for cancer and is mainly used to monitor known ovarian cancer alongside imaging and clinical evaluation. Elevated CA‑125 requires further assessment to determine the cause.

Q: Is CA-125 good or bad?

A: CA‑125 is neither simply good nor bad; it's a blood biomarker that can be elevated in ovarian cancer but also in many benign conditions (endometriosis, menstruation, pregnancy, inflammation, liver disease). It’s most useful for monitoring known ovarian cancer or recurrence, not as a routine screening test in the general population. Results must be interpreted with clinical context and follow‑up by a clinician.

Q: Which blood test shows cancer?

A: No single blood test reliably detects all cancers. Certain blood tests can suggest cancer: tumor markers (PSA for prostate; CA‑125 for ovarian; CEA for colorectal; AFP for liver/testicular), an abnormal complete blood count for leukemia, and circulating tumor DNA (liquid biopsy) for mutation detection. Elevated markers prompt imaging and tissue biopsy, which are required to confirm a cancer diagnosis.