Cushing's Syndrome – Biochemical Tests	

The biochemical hallmark of the condition is inappropriate cortisol secretion. The biochemical features, however, can also be associated with psychological or physical stress, alcoholism, coma, depression, and obesity, while Cushing's syndrome itself may also be intermittent or cyclical. 
The diagnosis of Cushing's syndrome relies upon the demonstration of excessive cortisol secretion and abnormal feedback regulation of the hypothalamic-pituitary-adrenal axis. 
Loss of the normal circadian pattern of cortisol secretion, and lack of dexamethasone suppressibility (0.5mg administered orally precisely every six hours for two days), is characteristic of the disease (Fig. 8.12), but can be mimicked by the conditions described above. 

See also:
• Clinical Features of Cushing's Syndrome