What is the impact of dexamethasone on the cosyntropin (Corticropin) stimulation test?

From the Guidelines

Dexamethasone can significantly impact the results of a cosyntropin stimulation test and should be discontinued before testing. For accurate results, dexamethasone should be stopped at least 24-48 hours prior to the test, with longer washout periods (up to 1 week) being preferable when clinically feasible. This is because dexamethasone is a potent synthetic glucocorticoid that suppresses the hypothalamic-pituitary-adrenal (HPA) axis, which can lead to false-positive results suggesting adrenal insufficiency.

Key Considerations

• Dexamethasone works by providing negative feedback to the hypothalamus and pituitary, reducing ACTH production, which subsequently decreases endogenous cortisol production 1.
• During a cosyntropin test, synthetic ACTH (cosyntropin) is administered to stimulate the adrenal glands to produce cortisol.
• If a patient has been taking dexamethasone, their adrenal glands may be temporarily suppressed and unable to respond appropriately to the cosyntropin stimulus, even if their adrenal function is intrinsically normal.
• Measuring dexamethasone level along with cortisol the morning after 1 mg dexamethasone ingestion improves test interpretability 1.

Clinical Implications

• If dexamethasone cannot be discontinued before testing due to clinical necessity, this should be clearly documented and considered when interpreting the results, as the test may not accurately reflect the patient's true adrenal function.
• The use of dexamethasone in patients with Cushing's disease or other forms of hypercortisolism can affect the results of diagnostic tests, including the cosyntropin stimulation test 2.
• A non-invasive approach using a combination of laboratory and imaging tests, such as CRH and desmopressin stimulation, MRI, and whole-body CT, may be useful in distinguishing between pituitary and ectopic ACTH-secreting tumors 2.

From the FDA Drug Label

DRUG INTERACTIONS • Drug effects on plasma cortisol levels: o Accuracy of the test results can be affected by concomitant medications. o Glucocorticoids and spironolactone: May falsely elevate plasma cortisol levels. Stop these drugs on day of cosyntropin for injection testing Long-acting glucocorticoids may need to be stopped for a longer period before cosyntropin for injection testing.

The impact of dexamethasone, a type of glucocorticoid, on the cosyntropin (Corticropin) stimulation test is that it may falsely elevate plasma cortisol levels. To ensure accurate test results, glucocorticoids like dexamethasone should be stopped on the day of testing, with long-acting glucocorticoids potentially needing to be stopped for a longer period before the test 3.

From the Research

Impact of Dexamethasone on Cosyntropin Stimulation Test

• The cosyntropin stimulation test is used to assess adrenal function, and dexamethasone can affect the results of this test 4, 5.
• A study found that dexamethasone therapy can suppress the cortisol response to the cosyntropin stimulation test, but this effect may not be significant within the first 72 hours of therapy 4.
• The study suggests that the cosyntropin stimulation test can be used to diagnose adrenal insufficiency within the first 3 days after initiation of dexamethasone therapy, but additional studies are needed to confirm these results 4.
• Other studies have compared the use of low-dose and high-dose cosyntropin stimulation testing in children and adults, and found that the choice of dose may not affect the diagnostic accuracy of the test 6, 7.
• The use of free cortisol measurements may add value to the diagnostic workup, particularly in patients with optimal dexamethasone concentrations and post-DST total cortisol between 1.8 and 5 mcg/dL 8.

Diagnostic Considerations

• The cosyntropin stimulation test should be interpreted cautiously, taking into account the patient's history and other diagnostic tests 5, 6.
• The choice of cosyntropin dose and the interpretation of test results may depend on the specific clinical context and the patient's individual characteristics 6, 7.
• Further studies are needed to determine the optimal approach to diagnosing adrenal insufficiency and to establish clear guidelines for the use of the cosyntropin stimulation test in different populations 4, 6, 7.