CA-125 Protein (Cancer Antigen 125) Quantitative
This test measures the level of CA-125, a protein found in higher amounts in some cancers of the ovaries, uterus, and other reproductive organs, as well as in some non-cancerous conditions.
["CA-125 levels help monitor ovarian cancer and other related conditions, often used alongside other tests for early detection or treatment follow-up."]
Key facts at a glance
- LOINC
- 40618-1
- Short code
- CA125PF
- Synonyms
- Cancer Ag125 Prt-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Sterile, leak-proof container (red-top or SST tube acceptable); plain sterile container for fluid collection
- Units
- N/A
- Critical range
- 0.5 N/A – —
- Fasting
- false
- Population
- adult
- Sex
- female
- Age range
- 18–99 years
- Method
- Immunoassay (Chemiluminescent or Electrochemiluminescent)
- CPT
- 86304
- SNOMED
- 104737003
- Specimen volume
- 5-10 mL of peritoneal fluid
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 3 months. Avoid repeated freeze-thaw cycles.
- 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 in the context of ovarian cancer screening, surveillance, and treatment monitoring. It may also be checked in patients with symptoms suggestive of gynecological cancers or other conditions affecting the reproductive organs. However, CA-125 alone is not a definitive diagnostic test for ovarian cancer and is often used alongside imaging and other tests for a complete evaluation.
How Is the Test Performed?
A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it is analyzed to measure the CA-125 protein concentration. Results are reported in international units per milliliter (IU/mL).
Why Might Your Doctor Order This Test?
Your doctor may recommend a CA-125 test if you have symptoms like abdominal pain, bloating, or changes in bowel habits. It may also be used in ovarian cancer screening for high-risk individuals, during cancer treatment to monitor progression or response, or in follow-up care for patients with known gynecological cancers.
What Do Results Mean?
CA-125 levels vary widely and can be influenced by many factors, including pregnancy, menstrual cycles, and other health conditions. Elevated levels may suggest ovarian cancer or other gynecological cancers, but they can also be found in non-cancerous conditions. Your doctor will interpret results in the context of your medical history and other tests.
Reference range
No established reference range for peritoneal fluid; CA-125 in peritoneal fluid is interpreted in conjunction with serum CA-125 levels. Elevated levels may indicate malignant peritoneal involvement, particularly in ovarian carcinoma.N/A
No special patient preparation required. Specimen collection typically performed during abdominal paracentesis or peritoneal lavage procedure by qualified healthcare professional.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: CA-125 plays a key role in the management of ovarian cancer and related conditions. While it is not a definitive diagnostic test, it can help identify potential issues early and guide treatment decisions. Elevated levels may prompt further investigation, including imaging studies or additional blood tests. It is important to note that CA-125 levels alone are not sufficient for diagnosis and should be considered alongside clinical findings and other diagnostic tools.
Short name
CA-125 Test
Frequently asked questions
What does a high CA-125 level mean?
Can CA-125 levels change over time?
Is CA-125 the only test used to diagnose ovarian cancer?
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