How well does CA125 find ovarian cancer in GP care?
In UK primary care, CA125 ≥35 U/ml had high NPV but only about 10% PPV for ovarian cancer, and elevated values also flagged other cancers.
Source
The diagnostic performance of CA125 for the detection of ovarian and non-ovarian cancer in primary care: A population-based cohort study
Study at a glance
- Design
- Cohort — Population-based primary-care EHR cohort
- N
- N=50780 · Women with CA125 tested in English primary care
- Population
- Women having CA125 measured in English general practice
- Outcome
- PPV, sensitivity, specificity, and AUC of CA125 ≥35 U/ml for ovarian cancer
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Inspect source passages
How well does CA125 find ovarian cancer in GP care?
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At ≥35 U/ml, PPV 10.1%, sensitivity 77.0%, specificity 93.8%
At or above the 35 U/ml cutoff, CA125 demonstrated a PPV of 10.1% (95% CI 9.1–11.2), an NPV of 99.8% (95% CI 99.7–99.8), a sensitivity of 77.0% (95% CI 72.8–80.8%) and a specificity of 93.8% (95% CI 93.6–94.0) for ovarian cancer.
Cohort of 50,780 women; ovarian cancer incidence 0.9%
The ovarian cancer incidence in the cohort was 0.9% and was 3 times higher in the ≥50 years group than the <50 years group ( ).
What they did
Researchers studied 50,780 women who had CA125 tested in English primary care, linking results to cancer diagnoses. They estimated diagnostic accuracy at the conventional ≥35 U/ml cutoff and examined age-stratified performance and non-ovarian cancers.
What they found
Ovarian cancer incidence was 0.9%. At ≥35 U/ml, PPV was 10.1%, sensitivity 77%, specificity 93.8%, and AUC 0.92. Performance and cancer mix varied by age; elevated CA125 also related to non-ovarian cancers.
The limits
What it doesn't show
Observational EHR data cannot prove that changing CA125 thresholds or pathways improves survival, and symptom recording is incomplete.
Key terms
- CA125
- Cancer antigen 125 blood biomarker used to investigate possible ovarian cancer.
- PPV
- Positive predictive value—probability of disease given a positive test.
- NPV
- Negative predictive value—probability of no disease given a negative test.
- Sensitivity
- Proportion of true cases correctly identified by the test.
- AUC
- Area under the ROC curve summarizing discrimination across thresholds.
- Primary care testing
- Investigations ordered by general practitioners before specialist referral.
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In this primary-care cohort, PPV of CA125 ≥35 U/ml for ovarian cancer was about:
Common questions
What cutoff was evaluated?
The standard clinical cutoff of ≥35 U/ml.
Is a positive CA125 usually ovarian cancer?
No—PPV was about 10%, so most positives are not ovarian cancer.
Is a negative test reassuring?
NPV was very high (99.8%), though no test is perfect.
Why mention non-ovarian cancers?
Elevated CA125 can accompany other malignancies that clinicians should consider.
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