Synacthen stimulation test

Low plasma cortisol levels and high levels of ACTH are found. One of the essential findings is that the patient does not respond in the Synacthen stimulation test. Other biochemical findings are hypoglycaemia and hyponatraemia. 

The synacthen stimulation test illustrates the principle behind these tests. In normal persons, administration of synacthen (a synthetic form of ACTH) results in stimulation of the adrenal cortex and a subsequent rise in the plasma cortisol level. When there is adrenocortical hypofunction, as in Addison s disease, the rise in the plasma cortisol level doe not occur or is markedly reduced. 

Synacthen (tetracosactrin) is a synthetic peptide having ACTH activity. It is used in the diagnosis of adrenocortical hypo-function. Injection of synacthen should normally result in an increase in plasma cortisol levels after 30 minutes as a result of stimulation of the adrenal gland. An impaired response suggests adrenocortical hypofunction. A further test may then be performed in order to distinguish between primary adrenocortical hypofunction (Addison s disease) and secondary adrenocortical hypofunction. This consists of three injections of synacthen on successive days. An improvement in cortisol production indicates secondary adrenocortical hypofunction. No improvement occurs if there is primary adrenocortical insufficiency. 

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