Reference Range. 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.eference Range. 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).