Part of “CHAPTER 72 – SYNTHESIS AND METABOLISM OF CORTICOSTEROIDS“

Generally, it is the total level of a hormone that is measured. Many factors can alter binding globulin concentrations in plasma38 (see Table 72-4). Because the free hormone determines biologic activity, knowledge of the conditions affecting the binding proteins is important in assessing total serum steroid levels. Sex steroids—in particular, estrogen—increase CBG levels. Therefore, in pregnant women or women taking oral contraceptives, higher circulating serum cortisol levels are expected, although free cortisol and cortisol activity should be normal. Thyroid hormone also stimulates CBG synthesis. Some families appear to have inherited elevations in CBG levels; elevations may also be seen in diabetes mellitus. Subnormal levels are seen in states of decreased protein production, such as in liver disease, or in states of protein loss (e.g., the nephrotic syndrome). Some patients have heritable varients in their CBG, resulting in low cortisol-binding affinity.38a Hypothyroidism, multiple myeloma, and obesity have all been associated with low circulating CBG levels. The circulating concentration of TeBG is affected by age, body weight, and circulating estrogen, testosterone, and thyroid hormone levels.