CA-125 Tumor Marker (Serum) – Quantitative
This test measures the level of CA-125, a protein produced by some cancer cells, often used to monitor ovarian, endometrial, or other gynecologic cancers.
["CA-125 helps track cancer progression or response to treatment in certain cancers."]
Key facts at a glance
- LOINC
- 19165-0
- Short code
- CA125PF
- Synonyms
- Cancer Ag125 Plr-aCnc
- Category
- chemistry
- Sample
- fluid
- Container
- Sterile, leak-proof pleural fluid collection container (e.g., red-top vacutainer tube or sterile specimen cup without anticoagulant preferred)
- Units
- N/A
- Ref low
- 0
- Ref high
- 35
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86304
- SNOMED
- 11525-1
- Specimen volume
- 2-5 mL of pleural fluid
- Stability
- Stable for 24 hours at room temperature (20-25°C), 7 days refrigerated (2-8°C), and 3 months frozen at -20°C. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 300
- TAT
- 24–72 hours
- Order
- routine
Why This Test Is Done
Your doctor may order a CA-125 test to check for signs of cancer, especially ovarian or endometrial cancer, or to monitor existing cancer. It can also help determine if treatment is working or if cancer has returned. Note that CA-125 levels can also rise in non-cancer conditions like endometriosis or pelvic infections, so results should be interpreted by a healthcare provider in context with your medical history and symptoms.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw blood, which usually causes only mild discomfort. Avoid strenuous activity or eating/drinking for 2–3 hours before the test if instructed by your doctor.
What the Test Results Mean
CA-125 results alone are not diagnostic for cancer. Elevated levels may indicate cancer but can also occur in other conditions. Your doctor will consider your symptoms, medical history, and other test results to interpret the meaning of your CA-125 level.
Common Conditions That May Affect Results
CA-125 can be elevated in ovarian cancer, but it is not specific to this cancer. Other conditions, such as endometriosis, pelvic inflammatory disease, or liver disease, may also cause higher-than-normal levels. Always discuss your results with your healthcare provider.
Reference range
No established reference range for pleural fluid; serum reference (<35 U/mL) typically used as a guide. Elevated levels in pleural fluid may suggest malignant effusion, particularly ovarian or other gynecologic malignancies.N/A
No special patient preparation required prior to thoracentesis. Inform the ordering physician of any recent surgeries, infections, or active inflammatory conditions that may affect CA 125 levels.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
CA-125
Frequently asked questions
What does a high CA-125 level mean?
Can a low CA-125 level rule out cancer?
How often should I get a CA-125 test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy