Reference range (ca-125)

NICE have state age and serum CA125 thresholds (1):

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The NICE committee noted (1):

1. Moderate-certainty evidence showed that in women over 50, serum CA125 levels meet the predictive value needed to justify a strong recommendation to arrange an ultrasound scan. Based on the clinical and health economic evidence, the committee agreed age-specific thresholds in 10-year age bands for this age group.
2. For people aged 40 to 49 years, although the evidence was less certain and did not meet the required predictive value needed to justify a strong recommendation to arrange an ultrasound scan, the CA125 threshold of 35 U/ml or over still shows moderate‑to-high sensitivity. The committee agreed that for this age group, the measurement of CA125 remains useful in guiding decisions about further investigations.
3. The low prevalence of ovarian cancer in younger age groups affects serum CA125 performance, which increases the risk of false reassurance and late diagnosis, particularly in those aged 39 and under. For this age group, the committee agreed that serum CA125 is not sufficiently accurate to support decision making. Therefore, the committee recommended that serum CA125 should not be used in isolation to guide suspected ovarian cancer decisions. The committee recommended considering an ultrasound scan for those with persistent symptoms. The committee also agreed the importance of safety netting for those aged 39 and under, and recommended that if an ultrasound scan is normal, other potential causes of symptoms should be investigated and people advised about when to return to their GP.

Reference:

1. NICE (April 2026). Suspected cancer: recognition and referral.