From the Guidelines
A low fasting cortisol level with a normal response to cosyntropin stimulation is indicative of secondary adrenal insufficiency, suggesting that the adrenal glands are functioning properly when stimulated, but are not receiving adequate signals from the pituitary gland. This condition typically requires further evaluation by an endocrinologist to determine the underlying cause, which may involve measuring ACTH levels and possibly pituitary imaging to check for tumors or other abnormalities affecting the hypothalamic-pituitary axis 1.
Key Considerations
- The patient should be aware of symptoms like fatigue, weakness, dizziness, and nausea, which could indicate cortisol deficiency.
- In stressful situations such as illness or injury, supplemental hydrocortisone may be necessary, typically 15-25mg daily in divided doses, but this should only be initiated under medical supervision 1.
- The distinction between primary and secondary adrenal insufficiency is crucial, as treatment approaches differ, with secondary forms often requiring treatment of the underlying pituitary or hypothalamic disorder rather than just cortisol replacement.
Treatment and Management
- Patients with secondary adrenal insufficiency may require hydrocortisone replacement therapy, with doses ranging from 15-25mg daily in split doses 1.
- It is essential to educate patients on managing daily medications and situations of minor to moderate concurrent illnesses, and to provide supplies for self-injection of parenteral hydrocortisone in case of emergencies.
- Regular follow-up with an endocrinologist is necessary to assess health and well-being, measure weight, blood pressure, and serum electrolytes, and monitor for potential complications of glucocorticoid therapy.
From the Research
Significance of Low Fasting Cortisol Level
- A low fasting cortisol level with a normal response to cosyntropin (adrenocorticotropic hormone) stimulation in a patient not taking any corticosteroids (steroids) may indicate relative adrenal insufficiency, which is an increasingly documented phenomenon in acute illness 2.
- The cosyntropin test remains a superb test of primary adrenal failure, but its utility in the diagnosis of secondary adrenal failure is less clearly defined 2, 3.
- A post-cosyntropin cortisol value greater than 20 microg/dl has been recognized as consistent with normal adrenal function 2, but a normal response to cosyntropin does not necessarily rule out adrenal insufficiency, especially in the setting of acute illness 2, 4.
Diagnostic Criteria
- A morning serum cortisol level >13 mcg/dL reliably rules out adrenal insufficiency, and the test is easy and safe to perform 4.
- The 1-microg cosyntropin stimulation test (CST) is more sensitive than the 250-microg CST for the diagnosis of secondary adrenal insufficiency in nonstressed patients 3.
- Basal cortisol levels ≤100 and ≥450 nmol/L have high diagnostic accuracy and may abolish the need for formal ACTH testing 5.
Clinical Implications
- Pending the availability of free cortisol levels, it is prudent not to disregard low basal cortisol levels, even in the presence of a normal cosyntropin response 2.
- Clinicians managing acutely ill patients should have a low threshold for initiating glucocorticoid replacement in the presence of hypoglycemia and shock, regardless of the peak cortisol values 2.
- Symptomatic hypocortisolemia may be present in severe hyperthyroidism, and it resolves with adequate treatment of the hyperthyroidism 6.