Sex-hormone-binding globulin (SHBG) is a B-globulin that specifically binds steroid hormones. The major site of SHBG synthesis is thought to be the hepatocytes. Its production is regulated by androgen/estrogen balance, thyroid hormones, insulin and dietary factors, among others. SHBG is involved in the transport of sex steroids in plasma. Its concentration is a major factor regulating their distribution between protein-bound and free states. Determination of SHBG concentration is mainly of importance in the evaluation of mild disorders of androgen metabolism and it allows identification of women with hirsutism who are likely to respond to estrogen therapy. Testosterone/SHBG-ratios correlate well with both measured and calculated values for free testosterone, and help to discriminate between subjects with excessive androgen activity and normal individuals.

In general the measurement of SHBG offers the possibility for calculating the free fraction of vatious steroid hormones based on the measurement of the total concentration in serum. But there is also a method available for the direct measurement of free steroid hormones in saliva. The metabolic activity of any steroid in any case is just represented by the free hormone fraction which represents less than 5% of the total. The non-invasive sampling of saliva samples offers another advantage of salivary testing.