1. Sex hormone binding globulin (SHBG) is a §-globulin that transports testosterone, dihydrotestosterone (DHT), and estradiol in plasma. It tightly binds approximately 60% of plasma testosterone and DHT. Neither steroid is metabolically active in the bound form. Therefore, SHBG, often performed together with the total testosterone, can be used to estimate the bioavailable testosterone levels. The major clinical ulitily of low SHBG levels is to aid in the diagnosis of hirsutism, acne vulgaris and polycystic ovary syndrome. In addition , modestly reduced values may be found in hyperprolactinemia, hypothyroidism, Cushing's disease, acromegaly and obesity. Elevated SHBG may be seen in hyperthyroidism, pregnancy, estrogen administration, some drugs and hepatitic cirrhosis. Clinical correlation is important in the interpretation of the results obtained from this assay.
2. Falsely decreased results may be seen in patients on high doses of biotin (i.e. > 5mg/day). Samples should only be collected from these patients at least 8 hours following the last biotin administration so as to avoid potential interference.