Binding of testosterone and estradiol in plasma

It has been shown that the two major active sex hormones, estradiol and testosterone, are bound with high affinity to a common site (or sites) on plasma globulin. The level of this protein is elevated slightly in portal cirrhosis and greatly in the later months of pregnancy. The high specificity and affinity of this protein for the sex hormones has enabled it to be used to provide a sensitive radioassay for their determination in small amounts of body fluids.