Adrenocorticotropic Hormone (ACTH) Stimulation Test
Adults
Basic Information 
• Take pre-ACTH administration blood sample in heparinized or plain tubes.
• Administer ACTH gel (1 IU/kg IM) between 8 and 10 am.
• Take post-ACTH blood samples 2 and 4 hours after ACTH administration.
• Horses with a functional adrenal cortex should have more than twofold increases in cortisol concentrations.
• In the cosyntropin stimulation test, 0.5 to 1 mg of synthetic ACTH (cosyntropin; Cortrosyn) is administered IV between 8 am and noon.
• Take pre-ACTH blood sample, administer cosyntropin, and take post-ACTH blood sample 2 hours later.
• Interpret as for the ACTH stimulation test.
• Cortisol should be twice baseline 2 hours later.
• A lack of cortisol response suggests adrenal insufficiency.
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