CA-125 Tumor Marker (Serum) with Fluid Dilution Confirmation
This test measures a protein called CA-125, which may be elevated in certain cancers, including ovarian cancer, and sometimes in other conditions affecting the abdomen or pelvis.
["CA-125 helps doctors monitor cancer progression or response to treatment, but it’s not a definitive diagnostic test alone."]
Key facts at a glance
- LOINC
- 15156-3
- Short code
- CA125BF
- Synonyms
- Cancer Ag125 Fld Dil-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top serum tube (no anticoagulant) or serum separator tube (SST)
- 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
- dilution
- CPT
- 86304
- SNOMED
- 104072004
- Specimen volume
- 1-2 mL serum
- Stability
- Stable for 24 hours at room temperature (15-25°C), 7 days at 2-8°C, and 3 months at -20°C or lower. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Doctors may order a CA-125 test to check for signs of ovarian cancer, especially if you have symptoms like bloating, pelvic pain, or unexplained weight changes. It can also be used during follow-up for known cancer patients or after surgery/treatment to track levels over time.
What to Expect Before the Test
No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific method. Bring any medications you’re taking, as some (like birth control) can affect results.
What the Test Results Mean
Elevated CA-125 levels often suggest ovarian cancer or other abdominal/pelvic issues, but they can also appear in benign conditions like endometriosis or pelvic inflammation. A single high result doesn’t confirm cancer—your doctor will consider symptoms, imaging, and other tests.
Common Conditions That May Affect Results
CA-125 can rise in non-cancerous conditions like endometriosis, fibroids, or infections. It may also increase after abdominal surgeries or during pregnancy.
Reference range
Reference range varies by specimen type. For serum: < 35 U/mL. For body fluids (peritoneal, pleural, peritoneal washings): No established reference range; results should be interpreted in conjunction with clinical findings and cytology. Elevated CA-125 in body fluids may suggest malignancy or inflammatory processes.N/A
No special preparation required. Specimen should be collected prior to initiation of chemotherapy or radiotherapy when possible, as treatment may affect results.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
CA-125 is a tumor marker used primarily to monitor ovarian cancer progression or recurrence. While not a screening test for healthy individuals, it helps track treatment response or detect early signs of spread. Levels may drop after successful treatment but can rise again if cancer returns.
Short name
CA-125 Test
Frequently asked questions
What does a CA-125 test measure?
Why might my CA-125 level be higher than expected?
Can I get false-positive or false-negative results?
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