Will starting hydrocortisone (corticosteroid) today affect my cortisol level test results tomorrow?

Impact of Hydrocortisone on Cortisol Level Testing

Yes, starting hydrocortisone today will significantly affect your cortisol level test results tomorrow, making them unreliable for diagnostic purposes. 1

How Hydrocortisone Affects Cortisol Testing

Hydrocortisone (synthetic cortisol) directly interferes with cortisol measurements in several important ways:

1. Cross-reactivity in assays: Hydrocortisone is chemically identical to endogenous cortisol and will be measured as cortisol in laboratory tests, artificially elevating results 1

2. Suppression of natural production: Exogenous hydrocortisone suppresses your body's natural cortisol production through negative feedback on the hypothalamic-pituitary-adrenal (HPA) axis

3. Timing considerations: The Endocrine Society guidelines clearly state that "AM cortisol in a patient on corticosteroids is not diagnostic as the measurement of therapeutic steroids in the assay for cortisol varies" 1

Required Washout Period

For accurate cortisol testing:

• Hydrocortisone must be held for at least 24 hours before measuring endogenous cortisol function 1
• Other steroids require even longer washout periods before testing 1
• Without this washout period, results will be uninterpretable and potentially misleading

Clinical Implications

Starting hydrocortisone before cortisol testing can lead to:

• False elevations in measured cortisol levels due to the medication itself
• Masking of adrenal insufficiency that might require treatment
• Inaccurate diagnosis of your cortisol status, potentially affecting treatment decisions

Special Considerations

• If you need to start hydrocortisone urgently for clinical reasons (e.g., suspected adrenal crisis), treatment should not be delayed for testing 1
• In such cases, alternative diagnostic approaches may be needed later
• For patients already on corticosteroids for other conditions, endocrinology consultation is recommended for recovery and weaning protocols using hydrocortisone 1

Recommendations

1. Postpone hydrocortisone until after your cortisol testing is complete
2. Complete cortisol testing first, then start hydrocortisone if indicated
3. If hydrocortisone treatment is urgently needed, discuss with your doctor about alternative diagnostic approaches or rescheduling the test

Following these recommendations will ensure accurate test results that can properly guide your treatment decisions.