ABSTRACT
Estradiol (E(2)) - similarly to testosterone - is a hormone mainly bound to SHBG and albumin in serum. Only the non SHBG-bound (free and albumin-bound hormone, i.e. bioavailable) hormone diffuses easily from circulation to tissues and is available for target cells. Bioavailable hormone measured or calculated seems to represent the best access to bioactive hormone concentration. Several studies reported that this bioavailable E(2) could be usefully measured for the understanding of chronic diseases in men or women, such as osteoporosis, cardiovascular disease and Alzheimer's disease. E(2) assays require a high sensitivity to assess low concentrations. It is currently difficult to know if bioavailable E(2) is really implicated or not in a given pathology but its interest is reported in many epidemiological studies.
Subject(s)
Alzheimer Disease/blood , Estradiol/blood , Osteoporosis/blood , Sex Hormone-Binding Globulin/metabolism , Adult , Age Factors , Aged , Aging , Alzheimer Disease/diagnosis , Biological Availability , Biomarkers , Bone Density , Estradiol/physiology , Female , Fluorescence , Humans , Immunoassay , Luminescence , Male , Middle Aged , Osteoporosis/diagnosis , Osteoporosis/metabolism , Pregnancy , Risk Factors , Sex Factors , Testosterone/bloodABSTRACT
Serum cortisol free fraction is responsible for its physiological function. Determination of serum total cortisol concentration does not allow accurate evaluation of hypothalamic pituitary adrenal axis when there is a quantitative variation in serum transcortin. Although free cortisol can be assayed by salivary or urinary cortisol measurements, these methods can not be easily applied in intensive care units. Free plasmatic cortisol measurement could provide a better reflect of circulating cortisol in patients with critical illness whom have a decreased concentration of binding proteins and whom adrenal status is an important prognostic factor. Free cortisol can be measured after separation from bound cortisol, calculated with equation based on equilibrium binding or evaluated by cortisol/CBG ratio. In various studies, free plasmatic cortisol allows in critical care patients a better appreciation of adrenal status than total cortisol and be more differential than total cortisol increment after stimulation with synacthen used to diagnose "relative adrenal insufficiency".
