Skip to content

CA-125 (Cancer Antigen 125) Serum Immunoassay

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of CA-125, a protein linked to certain types of ovarian cancer and other gynecologic or non-gynecologic malignancies. It’s often used to help detect, monitor, or assess recurrence of these cancers.

Quick summary

["CA-125 helps track cancer progression or response to treatment but isn’t a definitive diagnostic test alone."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
83082-8
Short code
CA125
Synonyms
Cancer Ag125 SerPl IA-aCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top clot tube; plasma may be collected in lithium heparin or EDTA tubes
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 (e.g., Chemiluminescent, Electrochemiluminescent, or ELISA)
CPT
86304
SNOMED
115269000
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. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
100
Icterus max
50
TAT
4–24 hours
Order
routine

What Is CA-125 Used For?

CA-125 is primarily used in the context of ovarian cancer screening, surveillance, and follow-up. It may also be checked in patients with other suspected cancers, such as those of the uterus, fallopian tubes, or peritoneal lining, or in individuals with symptoms like persistent abdominal pain or bloating. Doctors may use it alongside other tests to guide treatment decisions or assess disease activity.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The blood is processed to separate serum (the liquid part) for testing. The CA-125 level is measured using an immunoassay method, which detects the protein in your blood.

What Might Elevated or Low Levels Indicate?

Elevated CA-125 levels are most strongly associated with ovarian cancer, though they can also appear in other cancers or conditions, such as endometriosis, pelvic inflammatory disease, or liver disease. Low levels typically suggest no active cancer or a non-cancerous cause. However, results alone don’t confirm a diagnosis—your doctor will consider them alongside other test results and clinical findings.

How Often Is This Test Done?

The frequency depends on your medical history and treatment plan. For ovarian cancer screening in high-risk individuals, it may be done periodically (e.g., every 6–12 months). For monitoring cancer progression or treatment response, it could be checked more regularly or after specific triggers (e.g., post-surgery or chemotherapy). Always follow your healthcare provider’s recommendations.

Reference range

Less than 35 U/mL is generally considered normal for healthy adults. Reference values may vary slightly by laboratory and assay manufacturer. Values above 35 U/mL may indicate the presence of malignancy or other conditions and should be interpreted in conjunction with clinical findings and imaging studies.N/A

Specimen: serum

No special patient preparation required. Fasting is not necessary. However, patients should inform their healthcare provider of any medications, recent surgeries, or concurrent conditions (e.g., menstruation, pregnancy, pelvic inflammatory disease) that may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Limitations and Context

Short name

CA-125 Screening/Monitoring

Frequently asked questions

Why might my CA-125 test result be confusing or inconclusive?
CA-125 is not a perfect test. It can be elevated in non-cancerous conditions, and some cancers (like breast or lung cancer) may not raise CA-125 levels. False positives or negatives can occur, especially if other tests or symptoms are involved. Your doctor will interpret results in the context of your overall health, symptoms, and other diagnostic findings.
Can CA-125 be used to diagnose ovarian cancer?
No, CA-125 alone cannot diagnose ovarian cancer. It’s often used alongside other tests, such as ultrasounds, CT scans, or tumor markers like CA-19-9, to help assess suspicion. If your doctor suspects ovarian cancer, further evaluation will be needed.
What if my CA-125 level is high but I don’t have cancer?
High CA-125 levels can occur in conditions like endometriosis, pelvic infections, or liver disease. If your levels are elevated, your doctor will investigate further to rule out cancer or other causes. Lifestyle factors (e.g., obesity) may also influence results, so they’ll consider these in their assessment.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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