Cosyntropin (tradename Cortrosyn) is a synthetic derivative of ACTH that is used in the evaluation and diagnosis of cortisol disorders. Cosyntropin contains the first 24 (of a total 39) amino acids of ACTH but retains full function.
In patients with low cortisol levels or symptoms of adrencortical insufficiency, cosyntropin can be used to diagnose Addison's disease. A failure for serum cortisol levels to increase after administration of cosyntropin makes a diagnosis of primary adrenocortical insufficiency more likely. An increase in cortisol upon administration of cosyntropin rules out the condition.