Patient Preparation and Specimen Collection:
After an overnight fast, a serum sample is collected. Immediately afterwards, an injection of 250 micrograms of cosyntropin (Cortrosyn) is given IV (suspended in 2-5 mL of sterile normal saline) or IM. Additional serum samples are collected 30 and 60 minutes after the injection.
Testing:
The specimens can be tested for cortisol and ACTH. Samples can also be tested for other adrenal steroids.
Interpretation
Normal persons show a rapid rise in cortisol to the injected ACTH analogue:
(1) baseline cortisol > 5 µg/dL
(2) peak response after cosyntropin > 20 µg/dL
To distinguish between primary and secondary adrenal insufficiency, additional testing (prolonged ACTH test or plasma ACTH measurements) should be performed.
(1) Patients with adrenal destruction show no change in serum cortisol levels after ACTH injection; a normal cortisol response usually rules out primary adrenal insufficiency
(2) Patients with secondary adrenal insufficiency (atrophy of adrenal cortex due to exogenous glucocorticoid treatment, dysfunction of pituitary gland or hyphothalamus) usually have a slight rise in serum cortisol but the rise is less than normal. They usually have an inadequate response to the injected cosyntropin but occasionally they can have a normal response. Thus the rapid ACTH test should not be used alone to exclude secondary adrenal insufficiency.
(3) Primary adrenal insufficiency can be distinguished from secondary adrenal insufficiency by measuring ACTH in the specimen prior to cosyntropin injection, but the insulin tolerance test is considered superior for this purpose.
Inadequate responses to injected cosyntropin can be seen in:
(1) AIDS
(2) patients receiving ketoconazole
(3) treatment with steroids prior to testing
(4) adrenal carcinoma
