What dose of steroids, such as dexamethasone, should be given to a patient with a complex medical history, including potential hormone-sensitive cancers or cardiovascular disease, before drawing an Adrenocorticotropic Hormone (ACTH) stimulation test?

Steroid Dosing Before ACTH Stimulation Testing

You should NOT give steroids before drawing an ACTH stimulation test—doing so will invalidate the test by suppressing the HPA axis and causing false results. 1

Critical Principle: No Steroids Before Testing

Exogenous therapeutic steroids (including dexamethasone, prednisone, prednisolone, and inhaled corticosteroids like fluticasone) will suppress the hypothalamic-pituitary-adrenal axis and interfere with ACTH stimulation testing, requiring discontinuation before testing. 2, 1

• Morning cortisol measurements in patients actively taking corticosteroids are not diagnostic because the assay measures both endogenous cortisol and therapeutic steroids, with cross-reactivity varying by assay 1
• Laboratory confirmation of adrenal insufficiency should not be attempted in patients given corticosteroids until treatment is ready to be discontinued and sufficient washout time has elapsed 1
• Patients on corticosteroids will have low morning cortisol as a result of iatrogenic secondary adrenal insufficiency—this is expected and not diagnostic 1

Required Washout Periods

Hydrocortisone must be held for 24 hours before testing, while other steroids including prednisone require longer washout periods before endogenous adrenal function can be accurately assessed. 3, 1

• Wait until the patient has been weaned off corticosteroids before performing definitive HPA axis testing 3
• In cases of long-term steroid exposure, consult endocrinology for a recovery and weaning protocol using hydrocortisone rather than attempting abrupt discontinuation 1

Exception: Dexamethasone in Emergency Situations

If you must treat suspected adrenal crisis but still want to perform diagnostic testing later, use dexamethasone 4 mg IV instead of hydrocortisone, as dexamethasone does not interfere with cortisol assays. 1

• This is the ONLY scenario where giving a steroid before testing is appropriate—when the patient is critically ill and you cannot delay treatment 1
• Dexamethasone allows you to stabilize the patient while preserving the ability to measure endogenous cortisol production 1

Standard ACTH Stimulation Test Protocol

The recommended test uses 0.25 mg (250 mcg) cosyntropin administered IV or IM, with cortisol measured at baseline, 30 minutes, and 60 minutes post-administration. 2, 1

• A peak cortisol <500 nmol/L (<18 μg/dL) at either 30 or 60 minutes is diagnostic of adrenal insufficiency 2, 1
• A peak cortisol >550 nmol/L (>18-20 μg/dL) is considered normal and excludes adrenal insufficiency 1
• The high-dose (250 mcg) test is recommended over the low-dose (1 mcg) test due to easier practical administration, comparable diagnostic accuracy, and FDA approval 2, 1

Critical Pitfall to Avoid

Never attempt diagnostic testing while the patient is still on corticosteroids or immediately after stopping—this will yield false-positive results showing "adrenal insufficiency" that simply reflects expected HPA suppression. 1

• In cases of clinical uncertainty with ongoing steroid use, opt for empiric glucocorticoid replacement and test for ongoing need at 3 months rather than attempting diagnostic testing while on steroids 3
• ACTH stimulation can give a false-negative result early in hypophysitis as adrenal reserve declines slowly after pituitary stimulation is lost 3

When Treatment Cannot Wait

Treatment of suspected acute adrenal insufficiency should NEVER be delayed for diagnostic procedures—if the patient is clinically unstable with suspected adrenal crisis, give IV hydrocortisone 100 mg immediately plus 0.9% saline infusion. 3, 2, 1

• Draw blood for cortisol and ACTH before treatment if possible, but do not delay treatment to obtain samples 3, 1
• Mortality is high if adrenal crisis is untreated 1