Clinician reference tool — not medical advice. This is a clinical decision-aid intended for healthcare professionals: it gives deterministic suggestions to think with, not a diagnosis or a prescription. If you’re a patient, you’re welcome to look around — but please review anything here with your own doctor; it isn’t a substitute for personalized medical care.
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CA-125 (Cancer Antigen 125)

Tumour markers · specimen: blood

Indicated in specific situations

Also called: CA 125, CA125, cancer antigen 125, ovarian tumour marker, ovarian cancer marker

Chart note

Pick Ordered or Not ordered to see the note.

Indicated when

  • Evaluation of a known pelvic or adnexal mass found on exam or imaging, used alongside ultrasound to help triage which women need referral to gynecologic oncology [3]
  • Monitoring known epithelial ovarian cancer during and after treatment, under the direction of the treating gynecologic oncology team

Not indicated when

  • Screening for ovarian cancer in an asymptomatic woman at average risk, with no pelvic mass and no known high-risk hereditary cancer syndrome [1, 2]
  • General 'wellness' or tumour-marker panel with no pelvic finding and no personal history of ovarian cancer

Why not

In women without a known pelvic mass or ovarian cancer, CA-125 screening (alone or combined with transvaginal ultrasound) does not reduce ovarian cancer mortality, and the USPSTF found adequate evidence that it causes important harms, including many false-positive results that lead to unnecessary surgery in women who turn out not to have cancer [1]. Choosing Wisely Canada makes the same recommendation against screening average-risk asymptomatic women [2].

Better first step

Evaluate a pelvic complaint with a history and pelvic exam, and order pelvic/transvaginal ultrasound if a mass or persistent symptoms (bloating, early satiety, pelvic pain, urinary urgency) are present; if a mass is found, CA-125 alongside imaging is used to help decide who needs referral to gynecologic oncology [3]. For a patient with no mass and only vague symptoms, investigate those symptoms directly rather than ordering CA-125 as a screen.

Typical ND rationale

An ND may include CA-125 in a general women's health or hormone panel, reasoning that it is the well-known ovarian cancer marker and that checking it, especially with a family history of cancer or vague bloating or pelvic symptoms, offers early warning or reassurance.

Where the ND is right

Genuinely useful, combined with imaging, once there is an actual pelvic or adnexal mass to characterize and triage [3], and for monitoring known ovarian cancer under oncology direction. No validated screening role for CA-125 in a woman with a family history of breast or ovarian cancer but no mass and no confirmed hereditary syndrome was identified in this session; the more useful response to that family history is referral for hereditary cancer risk assessment rather than a stand-alone CA-125.

Ontario coverage & CONO orderability

OHIP status
uninsured
CA-125 is not listed by name in the 2026 Schedule of Benefits for Laboratory Services [5], so no OHIP fee code applies even when a physician orders it. A LifeLabs non-OHIP-billable test list republished by an Ontario hospital laboratory (effective June 2025) confirms CA-125 as a patient-paid, non-OHIP test in Ontario; this is used here as the secondary Ontario evidence the coverage rules call for when a test is absent from the Schedule [6]. ND-ordered testing is patient-paid regardless [7, 8]. (Secondary evidence: a community-lab price list, not a ministry statement. Hospital-lab funding for oncology follow-up is separate and was not checked.)
CONO orderable
Yes — CONO list #32
CONO list item 32, blood: 'CA125.'

Linked conditions

Counselling script

“CA-125 isn't a reliable screening test for otherwise healthy women, since it's often normal in early ovarian cancer and can be raised by common, harmless things like endometriosis or fibroids. If you have a pelvic mass we can feel or see on ultrasound, that's when CA-125 becomes useful, alongside imaging. If ovarian cancer runs in your family, let's talk about a referral for genetic risk assessment instead.”

Revisit if

  • A pelvic or adnexal mass is found on exam or imaging
  • New symptoms suggestive of ovarian cancer develop (persistent bloating, early satiety, pelvic or abdominal pain, urinary urgency)
  • A family history concerning for hereditary breast or ovarian cancer syndrome comes to light

References

  1. [1]US Preventive Services Task Force (2018). Screening for Ovarian Cancer: US Preventive Services Task Force Recommendation Statement. linkUSPSTF recommends against CA-125/ultrasound screening for ovarian cancer in asymptomatic average-risk women; harms include false positives leading to unnecessary surgery
  2. [2]Society of Obstetricians and Gynaecologists of Canada / Choosing Wisely Canada (2021). Obstetrics and Gynaecology recommendations. linkChoosing Wisely Canada: don't screen for ovarian cancer in asymptomatic women at average risk
  3. [3]Society of Obstetricians and Gynaecologists of Canada (2020). Guideline No. 403: Initial Investigation and Management of Adnexal Masses. linkInitial evaluation of an adnexal mass includes imaging and laboratory testing, in scope alongside CA-125, to triage women to gynecologic oncology
  4. [4]Canadian medical oncology societies / Choosing Wisely Canada (2025). Oncology recommendations. linkDon't order tests to detect recurrent cancer in asymptomatic patients without a realistic expectation that early detection improves survival, relevant to CA-125 monitoring after treated ovarian cancer
  5. [5]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkCA-125 is not listed by name in the 2026 OHIP Schedule of Benefits for Laboratory Services
  6. [6]LifeLabs (republished by Norfolk General Hospital laboratory) (2025). LifeLabs Non-OHIP Billable Test List (republished by Norfolk General Hospital laboratory, effective 2025). linkCA-125 appears on a LifeLabs Ontario non-OHIP-billable test list, i.e., patient-paid
  7. [7]Government of Ontario (e-Laws) (2026). Health Insurance Act, R.R.O. 1990, Reg. 552: General, s. 22 (insured laboratory services). linkA lab test is insured only when ordered by a physician, midwife, or NP who has clinically assessed the patient
  8. [8]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTests ordered by anyone other than an authorized provider, including NDs, are not insured services
Evidence notes

SOGC Guideline No. 403's full-text detail on exactly how CA-125 is combined with ultrasound (e.g., a formal Risk of Malignancy Index calculation) was not independently fetched this session; the journal's full text was access-restricted (HTTP 403) and only the PubMed abstract was quote-verified, which confirms CA-125 was in scope of the guideline's evidence review but not the precise algorithm. A reviewer should check the full guideline before publication. The commonly cited facts that CA-125 is elevated in roughly half of early-stage ovarian cancers, and that it can be raised by benign gynecologic conditions (endometriosis, fibroids, pelvic inflammatory disease) and pregnancy, are standard laboratory-medicine knowledge but were not independently quote-verified this session; flagged for reviewer confirmation before stating them as fact on a published page. Whether CA-125/ultrasound surveillance has a supported role in women at confirmed hereditary (e.g., BRCA) risk who have not yet had risk-reducing surgery was not established by a Canadian source this session; the USPSTF and Choosing Wisely Canada sources found both apply to average-risk or unspecified-risk women, so this record deliberately does not assert a position on the hereditary-risk case and instead points to genetics referral.