Primary Hyperadrenalism (Hypercortisolism)

Laboratory testing for the diagnosis of Cushing's syndrome can include the amount of free cortisol found in urine and blood samples, blood analysis for baseline values of ACTH, cortisol, CRH, and glucose, and dexamethasone suppression testing.

Cortisol is a steroid, fat-soluble hormone and is usually bound to cortisol-binding globulin proteins in the blood because fat-soluble proteins do not like aqueous environments. Normally there is a small amount of "free" cortisol that is unbound and will be filtered and removed as waste by the kidneys. This value is elevated in Cushing's syndrome because there is excess cortisol being produced. If the binding site of the proteins is full, then the remaining cortisol will spill into the peripheral blood. This large increase in "free" cortisol will be detectable in urine. Since the pathology lies with the adrenal gland, the blood hormone values for cortisol, ACTH, and CRH can be predicted to be high, low, and low respectively (see Table 5) as the body is attempting to stop cortisol production by lowering ACTH and CRH.