Typically, blood will be taken from a vein in the arm, but sometimes urine or saliva may be tested. Blood should ideally be collected between 8-9am when blood cortisol concentrations should be at their peak. A second sample may be taken late in the evening when cortisol should be at its lowest concentration (about midnight). Samples collected at these times allow the doctor to evaluate the daily pattern of cortisol secretion (the diurnal variation). This pattern may be disrupted with excess cortisol production – the maximum amount may be at or near normal concentrations, but levels may not fall as they should throughout the day. A single morning sample may be sufficient to detect decreased concentrations of cortisol.
Sometimes urine is tested for cortisol; this requires collecting all urine produced during a day ( 24-hour urine ). This sample will reflect the total amount of cortisol produced in the 24 hour period but will not allow doctors to evaluate variations in cortisol secretion.
CORTROSYN™ (cosyntropin) for Injection exhibits slight immunologic activity, does not contain animal protein and is therefore less risky to use than natural ACTH. Patients known to be sensitized to natural ACTH with markedly positive skin tests will, with few exceptions, react negatively when tested intradermally with CORTROSYN™. Most patients with a history of a previous hypersensitivity reaction to natural ACTH or a pre-existing allergic disease will tolerate CORTROSYN™. Despite this however, CORTROSYN™ is not completely devoid of immunologic activity and hypersensitivity reactions including rare anaphylaxis are possible. Therefore, the physician should be prepared, prior to injection, to treat any possible acute hypersensitivity reaction.
Interpretation: A rise from the baseline of at least 7 μg/dL to 10 μg/dL of cortisol, reaching at least 18 μg/dL at 60 minutes post stimulation effectively rules out primary adrenal insufficiency and suggests that adrenal suppression is minimal. A blunted or absent response suggests some level of secondary adrenal insufficiency (cortical atrophy or significant suppression.) If a subnormal response is obtained with an elevated baseline ACTH level, the patient has primary adrenal insufficiency or a form of ACTH unresponsiveness. A subnormal response with a low baseline ACTH level suggests CRF (corticotrophin releasing factor) and/or ACTH deficiency of hypothalamic and/or pituitary origin. Prior administration of estrogens, spironolactone, cortisone, and hydrocortisone (cortisol) can all interfere with the ACTH stimulation test by causing abnormally high baseline cortisol levels.