What does the Cancer Antigen 125 test measure?

Why is Cancer Antigen 125 measured?

CA 125 is the most widely used serum biomarker in ovarian cancer, both for pre-operative risk stratification in pelvic masses and for monitoring response to therapy and detecting recurrence in established epithelial ovarian cancer. Its sensitivity and specificity as a diagnostic tool are limited by benign gynaecological and non-gynaecological causes of elevation, so it is interpreted in context — a rising trend in a post-menopausal woman with a complex adnexal mass has different weight than an isolated elevation in a pre-menopausal woman with fibroids.

Reference ranges

Standard reference

<35 U/mL in most assays; post-menopausal and pre-menopausal thresholds may differ.

Functional medicine optimal

There is no single 'optimal' level; values remain stable and low in health. Serial measurement and trend matter more than a single result, particularly in surveillance.

Units

U/mL, kU/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.