Cancer antigen 125 (CA 125) is the only tumor marker recommended for clinical use in the diagnosis and management of ovarian cancer.
The reference range of CA 125 is 0-35 units/mL (0-35 kU/L).
The cutoff of 35 kU/L for CA 125 was determined from the distribution of values in healthy individuals to include 99% of the normal population.
The lack of an international standard for CA 125 hampers comparability among laboratories, and values derived from different methods are not interchangeable. As such, baseline levels in patients who undergo serial CA 125 monitoring should be redetermined if the methodology in the assay is changed.
Serum CA 125 values tend to decline with age and the onset of menopause. Levels also vary by race; concentrations tend to be lower in postmenopausal Asian and African women than in their white counterparts.