Cancer antigen 125 (CA125)
CA125 is a coelomic cell-surface glycoprotein of 200 kDa that is expressed on cells of serous ovarian carcinoma. CA125 is defined by the OC125 monoclonal antibody. It is expressed predominantly in ovarian cancer, though primary tumours of the endometrium, fallopian tubes, lung, breast, liver or gastrointestinal tract may also give rise to elevations of serum CA125.
Many other conditions aside from ovarian cancer may also cause increased levels, notably: endometriosis, menstruation, pelvic inflammatory disease, pregnancy, chronic hepatitis, congestive heart failure and poorly controlled diabetes. Higher levels (>100 kIU/L), or continuously increasing levels, are more specifically associated with ovarian cancer.
Ovarian cancer
Diagnosis: the 2011 NICE guideline established that CA125 testing was the most cost-effective strategy for early diagnosis of ovarian cancer. Screening for ovarian cancer in women at risk or with symptoms should be in combination with other modalities (ie. bimanual pelvic examination, transvaginal ultrasonography). CA125 and ultrasound measurements are used in calculating a risk of malignancy index for distinguishing benign from malignant pelvic masses.
Prognosis: pre- and post-operative CA125 measurements have prognostic value.
Treatment monitoring: baseline samples should be taken within 2 weeks prior to treatment and every 2-4 weeks during treatment. The rate of decline during initial therapy is a strong and independent prognostic indicator of response. A half-life of less than 20 days following chemotherapy correlates improved survival.
Surveillance: elevated or rising levels predict relapse.
Female: 0-35 kIU/L
Abbott Alinity
Please note: This test is now also available at Hillingdon, but UKAS accreditation for this site is pending.
Record last updated
September 5, 2025
Sample Container
5ml SST Vacutainers (Gold / Yellow top)
Sample Container
6ml Plain Vacutainers (Red top)
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Test Results
Yes, we have a Pathology User Guide
Yes. Please email your request to Imperial.nwlpcustomerservice@nhs.net
Results are communicated to clinical staff and are normally not communicated direct to patients either on telephone requests or in written report. If you need to contact us please click here to view the contact details page
Please contact the Customer Service Team Monday to Friday from 8:30am – 6:00pm on 0203 313 5353. Alternatively, see the Pathology User Guide for how to contact the relevant department. If advice is not urgent you can also email your query to Imperial.nwlpcustomerservice@nhs.net
Additional tests may be added by discussion with the relevant laboratory. The time limit for adding additional tests to a sample already received in the laboratory will depend on the type of sample and the department it was sent to.
Information on the repertoire of tests performed by pathology, including reference ranges, turnaround times and specimen requirements, can be found in the test directory.
Phlebotomy services are not managed by NWLP. For further information please see:
Imperial College Healthcare Trust Phlebotomy services
Chelsea and Westminster Hospital NHS Foundation Trust Phlebotomy services
NWLP operates UKAS accredited medical laboratories as per the references below. The current scope of accreditation for all NWLP’s laboratories can be found on the UKAS website.
See the following UKAS ref numbers:
- Clinical Biochemistry Ref: 8673
- Haematology and Blood Transfusion Ref: 8674
- Infection & Immunity Sciences (Including Immunology, Virology, Microbiology and Histocompatibility and Immunogenetics ) Ref: 8659
- Cellular Pathology (Including Histopathology, Cytology and Molecular Pathology) Ref: 9615
If you require copies of our certificate of accreditation and associated documentation please contact Imperial.nwlpcustomerservice@nhs.net.
UKAS requires the laboratories to be accredited for a particular repertoire/scope (ISO15189), any changes or additions to repertoire require assessment by UKAS (extension to scope).
The BD Hospital Tube Guide, BD GP Tube Guide and BD Paediatric Tube Guide provide visual references to the correct tube types and collection instructions.
Home testing
INSTRUCTION SHEET FOR BLOOD SAMPLE COLLECTION
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Our accreditations
Upholding excellence in diagnostic standards
Our laboratories are accredited by the UK Accreditation Service (UKAS) against the international standard ISO15189:2022. UKAS is the accreditation body for the UK that assesses medical laboratories.
Find out more about our accreditations on the UKAS website.
UKAS website