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Cancer Antigen 125 (Mucin 1) Serum/Plasma Concentration

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

This test measures the level of a protein called CA 125, which may be produced by certain types of cancer, including ovarian cancer. It can help monitor treatment progress or detect recurrence.

Quick summary

CA 125 levels may rise in some cancers but also in non-cancerous conditions; results should be interpreted by a healthcare provider in context.

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

Key facts at a glance

LOINC
13127-6
Short code
CA70K
Synonyms
Cancer Ag DM/70K SerPl-aCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube; plasma may be collected in heparin or EDTA tubes.
Units
N/A
Ref low
0
Ref high
5
Critical range
0.5 N/A – —
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Immunoassay (e.g., ELISA, Chemiluminescent Immunoassay)
CPT
86316
SNOMED
115341005
Specimen volume
1-2 mL of serum or plasma
Stability
Stable for 24 hours at 2-8°C; for longer storage, freeze at -20°C or below for up to 6 months. Avoid repeated freeze-thaw cycles.
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
24–72 hours
Order
routine

What Is CA 125 Used For?

CA 125 is primarily used as a biomarker for ovarian cancer screening, diagnosis, and monitoring. It may also help track response to treatment or identify recurrence. However, it is not a definitive test for cancer alone—results should be reviewed alongside clinical findings and imaging.

How Is This Test Performed?

A blood sample is drawn from a vein in your arm. The blood is then processed to separate serum or plasma, which is tested for CA 125 levels using an immunoassay method. Results are reported in arbitrary units per milliliter (U/mL).

What Does a High or Low Level Mean?

Elevated CA 125 levels may suggest ovarian cancer or other conditions like endometriosis, pelvic inflammation, or liver disease. However, many non-cancerous conditions can also cause elevated levels. Low levels are less commonly associated with cancer but may indicate normal health or other factors.

When Might You Need This Test?

Your doctor may order a CA 125 test if you have symptoms like abdominal pain, bloating, or irregular periods. It may also be used during cancer screening, follow-up care, or before surgery for ovarian cancer.

Reference range

Generally <5 U/mL (varies by laboratory and assay manufacturer); values vary depending on the specific CA 70K assay used.N/A

Specimen: serum

No fasting required. Inform the clinician of any recent diagnostic procedures (e.g., imaging with contrast) or medications that may affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: CA 125 is a tumor marker that can indicate ovarian cancer risk but is not specific enough alone to diagnose it. It is often used alongside other tests (like ultrasounds or CA 19-9) and clinical assessments. False positives or negatives can occur, so results should be discussed with your healthcare provider.

Short name

CA 125 (Mucin 1)

Frequently asked questions

Why might my CA 125 test be ordered if I don’t have cancer symptoms?
Your doctor may recommend it as part of routine monitoring for ovarian cancer risk, especially if you have a family history or other risk factors. It can also be used during treatment follow-up to check for changes in tumor size or recurrence.
Can CA 125 levels change without cancer?
Yes, elevated CA 125 can occur in non-cancer conditions like endometriosis, pelvic infections, or liver disease. Your doctor will consider your medical history and other test results before making a diagnosis.
How often should I get this test?
Frequency depends on your situation. If you have ovarian cancer, your doctor may recommend regular monitoring. If you’re at high risk, they may order it more often than standard screenings. Follow your healthcare provider’s guidance.
  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