When checking serum estradiol or testosterone, a total level that includes free and bound fractions can be assayed, or the free portion may be measured alone. Sex hormone-binding globulin can be measured separately from the total fraction of testosterone. A free androgen index expresses the ratio of testosterone to SHBG and can be used to summarize the activity of free testosterone. Affinity and binding Synonyms SHBG has been known under a variety of different names including: Sex hormone-binding globulin (SHBG) Sex steroid-binding globulin (SSBG, SBG) Sex steroid-binding protein (SBP, SSBP) Androgen-binding protein (ABP) Estradiol-binding-protein (EBP) Testosterone–estradiol binding globulin (TeBG, TEBG) References Further reading External links Glycoproteins