CA-125 Blood Test for Early Ovarian Cancer Detection

What is a CA-125 Blood Test for Ovarian Cancer?

The CA-125 blood test measures the serum levels of cancer antigen 125, a glycoprotein that is overexpressed in 80-90% of epithelial ovarian cancers, especially those of high-grade serous type. The normal range for CA-125 is <35 U/mL in healthy premenopausal women and <20 U/mL in postmenopausal women. Elevations above 65 U/mL should prompt diagnostic evaluation, which should be done in conjunction with a transvaginal ultrasound according to ACOG referral guidelines. Although the CA-125 test lacks sufficient sensitivity for general population screening, it is effective for risk stratification, treatment monitoring, and detecting recurrence 3-6 months before imaging.

How Does a CA-125 Blood Test Detect Ovarian Cancer?

Patient Preparation: No fasting is required for the test. A simple venipuncture collects 5-10 mL of serum in an SST tube. In premenopausal women, it is best performed mid-cycle (days 5-10) to minimize physiological fluctuations.

• •Laboratory Assay
  The test utilizes a two-site 'sandwich' enzyme-linked immunosorbent assay (ELISA) or a chemiluminescent immunoassay (CLIA) to detect the CA-125 antigen using OC125 monoclonal antibodies.
• •Reference Range Interpretation
  Age-adjusted cutoffs are applied (<65 U/mL for premenopausal and <35 U/mL for postmenopausal). Serial measurements showing a rise of >20% are considered suspicious.
• •Risk Assessment Integration
  The ROMA index combines CA-125 levels with HE4 and menopausal status to calculate a risk score. A score above 25% indicates the need for a referral to a gynecologic oncologist.
• •Diagnostic Confirmation
  An elevated CA-125 level should lead to a transvaginal ultrasound (TVUS) or CT scan. A significant drop (>90%) after chemotherapy confirms treatment response.

CA-125 Findings in Ovarian Cancer

• •Early-Stage (Stage I)
  Elevated in 50% of cases, with a mean level of 75 U/mL. Mucinous, clear cell, and endometrioid tumors may be CA-125 negative, requiring HE4 testing.
• •Advanced-Stage (Stage III/IV)
  Levels typically exceed 500 U/mL and correlate with peritoneal tumor burden. Pleural effusion can elevate levels further.
• •Non-Malignant Elevations
  Conditions like endometriosis (30%), fibroids, menstruation, and pelvic infections can lead to false positives; serial testing differentiates these from malignancy.

CA-125 by Ovarian Cancer Stages

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• •Stage I
  40-60% of patients show elevated levels; stage IA grade 1 is often normal (<35 U/mL).
• •Stage II
  70-80% of patients have abnormal levels (100-300 U/mL) as the disease extends to the pelvis.
• •Stage III
  90% have levels >100 U/mL, with omental disease yielding the highest values (500-2000 U/mL).
• •Stage IV
  Near-universal elevation (>95%); a doubling time of <3 months is associated with poor treatment response.

First CA-125 Test After Ovarian Cancer Treatment

• •Baseline Timing
  Conducted 4-6 weeks post-surgery or chemotherapy to establish a nadir. A decrease of >90% confirms treatment response per GCIG criteria.
• •Surveillance Frequency
  Every 2-3 months in years 1-2, every 3-6 months in years 3-5, and every 6-12 months thereafter per NCCN guidelines.
• •Monitoring Tips
  Focus on trends rather than absolute values. Avoid testing during infections. A rise of >25% or a fast doubling time should trigger imaging.

Why Choose Everhope for Ovarian Cancer CA-125 Blood Test?

Everhope Oncology uses high-sensitivity CLIA assays and provides comprehensive ROMA/HE4 panels. Our clinical process integrates serial CA-125 kinetics directly into a molecular tumor board review, correlating biomarker trends with TVUS/CT imaging for optimized surveillance and informed treatment decisions.