Cancer Antigen 125 (CA-125) Serum Immunoassay
This test measures the level of CA-125, a protein linked to certain types of ovarian cancer and other conditions affecting the ovaries, uterus, or peritoneum.
["CA-125 helps monitor cancer progression, treatment response, or recurrence in certain cancers."]
Key facts at a glance
- LOINC
- 15157-1
- Short code
- CA125
- Synonyms
- Cancer Ag125 SerPl Dil-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube for serum; lavender-top (EDTA) or green-top (heparin) for plasma
- Units
- N/A
- Ref low
- 0
- Ref high
- 35
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- female
- Age range
- 18–65 years
- Method
- dilution
- CPT
- 86304
- SNOMED
- 104734000
- Specimen volume
- 1-2 mL of serum or plasma
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is CA-125 Used For?
CA-125 is primarily used as a biomarker to detect or monitor ovarian cancer and other gynecological cancers. It may also be checked in patients with symptoms of peritoneal spread of cancer or other conditions affecting the pelvic organs, such as endometriosis or benign ovarian cysts, though these conditions do not always raise CA-125 levels significantly.
When Might You Need This Test?
Your healthcare provider may order a CA-125 test if you have symptoms like persistent abdominal pain, bloating, or unexplained weight loss. It may also be used as part of routine monitoring for ovarian cancer patients or those at higher risk due to family history.
What to Expect Before the Test
No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the blood draw if instructed by your doctor. Wear a comfortable shirt for easy access to your arm.
What Happens During the Test?
A healthcare professional will insert a small needle into a vein in your arm to collect a blood sample. You may feel a brief pinch, but the process is quick and typically painless.
Reference range
Normal: <35 U/mL. Values may vary slightly by laboratory and assay methodology.N/A
No special preparation required. Specimen collection is not affected by fasting status.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: CA-125 in Cancer Detection and Monitoring
Short name
CA-125 Blood Test
Frequently asked questions
Why is CA-125 Important in Cancer Care?
How Does CA-125 Help Track Cancer Treatment?
Does CA-125 Predict Cancer Risk?
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