Perform an ACTH Stimulation Test
The next step is to perform an ACTH stimulation test (cosyntropin test) to definitively assess the remaining adrenal gland's functional capacity and confirm whether this patient has developed secondary adrenal insufficiency from prolonged suppression of the contralateral gland.
Clinical Context and Interpretation
This 56-year-old man presents 6 months post-unilateral adrenalectomy with:
- Low morning cortisol (6.5 μg/dL) - below the normal range of 7-10 μg/dL
- Elevated ACTH (86 pg/mL) - appropriately elevated, indicating the pituitary is responding to low cortisol
This biochemical pattern suggests secondary adrenal insufficiency due to suppression of the remaining adrenal gland. Even though the mass was labeled as a "lipoma," the elevated ACTH with low cortisol indicates the removed gland was likely producing autonomous cortisol, suppressing the contralateral gland's function 1.
Why ACTH Stimulation Testing is Critical
The morning cortisol of 6.5 μg/dL falls in the indeterminate zone (between 3-10 μg/dL), where ACTH stimulation testing is specifically recommended to assess adrenal reserve 2, 3. The test will determine:
- Peak cortisol ≥18 μg/dL (500 nmol/L): HPA axis has recovered, no replacement needed 1
- Peak cortisol <18 μg/dL: Confirms adrenal insufficiency requiring glucocorticoid replacement 1
Management Algorithm Based on Test Results
If ACTH Stimulation Test Confirms Adrenal Insufficiency:
Initiate glucocorticoid replacement immediately:
- Hydrocortisone 15-20 mg daily in divided doses (typically 10 mg morning, 5-10 mg early afternoon) 1, 2
- Hydrocortisone is preferred over long-acting synthetic glucocorticoids to avoid prolonging HPA axis suppression 1
- Provide stress-dosing education and emergency injectable steroids 1, 2
- Issue a medical alert bracelet/card indicating adrenal insufficiency 2
Monitoring and Recovery:
- Recheck morning cortisol (before that day's dose) every 3 months 1
- Repeat ACTH stimulation testing when morning cortisol reaches ≥7.4 μg/dL (200 nmol/L) 1
- Most patients recover within 6-12 months, though some require longer 1, 4, 5
If ACTH Stimulation Test Shows Adequate Response:
- No glucocorticoid replacement needed
- Recheck morning cortisol in 3 months to ensure stability
- Counsel on symptoms of adrenal insufficiency to watch for
Critical Clinical Pearls
The "adrenal lipoma" diagnosis warrants scrutiny. The development of adrenal insufficiency 6 months post-surgery strongly suggests the removed mass was producing autonomous cortisol (mild autonomous cortisol secretion), which suppressed the contralateral gland 4, 5. True adrenal lipomas are exceedingly rare and typically non-functional.
Do not delay testing. Patients with cortisol levels in this range are at risk for adrenal crisis during physiologic stress (infection, surgery, trauma) 6, 3. The elevated ACTH indicates the pituitary is working appropriately, but the remaining adrenal may not be able to respond adequately to stress.
Avoid empiric steroid replacement without testing in stable patients, as this will further suppress the HPA axis and delay recovery 1. However, if the patient has symptoms of adrenal insufficiency (fatigue, weakness, nausea, hypotension, hyponatremia), initiate replacement immediately and confirm diagnosis later 3.