AM Cortisol: Which Tests to Order Alongside for a Complete Adrenal Workup

What Does an AM Cortisol Actually Measure?

An AM cortisol is a serum total cortisol measured during the physiologic peak of the hypothalamic-pituitary-adrenal (HPA) axis, typically between 6:00 and 8:00 a.m. Cortisol follows a circadian rhythm: levels spike shortly after waking (the cortisol awakening response), plateau briefly, then decline throughout the day to reach a nadir around midnight. The test captures the highest point of that curve.

Most commercial assays report total cortisol, which includes both the protein-bound fraction (roughly 80% bound to cortisol-binding globulin, or CBG, and 10% to albumin) and the free, biologically active fraction (about 10%). This distinction matters clinically. Oral estrogen, pregnancy, and hepatic disease all raise CBG, inflating the total number without changing free cortisol 1. In these patients, a calculated free cortisol or salivary cortisol (which measures only the unbound fraction) gives a more accurate reading.

A single AM cortisol below 3 mcg/dL is highly suspicious for adrenal insufficiency. A value above 15 to 18 mcg/dL (depending on the assay) generally rules it out. The gray zone between 3 and 15 mcg/dL is where paired testing becomes non-negotiable. The Endocrine Society's 2016 clinical practice guideline on adrenal insufficiency explicitly recommends against relying on a single basal cortisol when results fall in this intermediate range 2.

Plasma ACTH: The Single Most Important Co-Order

Every AM cortisol draw should include a simultaneous plasma ACTH. This one addition transforms an ambiguous number into a localizing tool. The logic is straightforward: ACTH is the pituitary signal that tells the adrenal cortex to produce cortisol, so the ratio between the two hormones reveals where the HPA axis has broken down.

Low cortisol with high ACTH (typically above 100 pg/mL) points to primary adrenal insufficiency, meaning the adrenals themselves are failing. Autoimmune adrenalitis (Addison disease) accounts for roughly 80% of cases in developed countries 3. Low cortisol with low or inappropriately normal ACTH signals secondary (pituitary) or tertiary (hypothalamic) insufficiency. The most common cause is abrupt withdrawal of exogenous glucocorticoids after prolonged use.

On the high side, elevated cortisol with suppressed ACTH suggests an autonomous adrenal source (adenoma, carcinoma, or bilateral macronodular hyperplasia). Elevated cortisol with elevated ACTH raises suspicion for Cushing disease (pituitary adenoma) or ectopic ACTH secretion from a neuroendocrine tumor 4.

ACTH is a fragile peptide. The sample must be collected in a pre-chilled EDTA (lavender-top) tube, placed on ice immediately, and centrifuged within 15 minutes. Failure to follow cold-chain handling degrades ACTH and produces falsely low results, a common preanalytical error that can mislead the entire workup.

DHEA-S and Adrenal Androgens

Dehydroepiandrosterone sulfate (DHEA-S) is produced almost exclusively by the zona reticularis of the adrenal cortex, making it a clean marker of adrenal androgen output. It is stable throughout the day (no circadian rhythm to worry about), inexpensive, and widely available.

In the context of a low AM cortisol, a low DHEA-S adds supporting evidence for primary adrenal insufficiency. The Endocrine Society notes that DHEA-S declines early in autoimmune adrenal destruction, sometimes before cortisol production drops below the reference range 2. It can serve as an early warning marker. A preserved DHEA-S in the setting of low cortisol and low ACTH is more consistent with recent-onset secondary insufficiency, where the adrenal reticularis has not yet atrophied.

In patients with suspected androgen excess (hirsutism, acne, irregular menses), DHEA-S helps separate an adrenal source from an ovarian source. A DHEA-S above 700 mcg/dL in a premenopausal woman warrants adrenal imaging to rule out an androgen-secreting adrenal tumor 5.

Order DHEA-S alongside AM cortisol when the clinical question involves adrenal reserve, unexplained androgen excess, or suspected early-stage autoimmune adrenal disease.

The Cosyntropin (ACTH) Stimulation Test

When the AM cortisol falls in the diagnostic gray zone (3 to 15 mcg/dL), the standard 250 mcg cosyntropin stimulation test is the next step. The patient receives an intravenous or intramuscular injection of synthetic ACTH1-24, and serum cortisol is measured at baseline, 30 minutes, and 60 minutes.

A peak cortisol of 18 mcg/dL or higher at either time point is considered a normal adrenal response. Failure to reach that threshold confirms adrenal insufficiency. The test has a sensitivity of approximately 97% for primary adrenal insufficiency when using the 250 mcg dose 6.

There is ongoing debate about whether the 1 mcg (low-dose) cosyntropin test is more sensitive for detecting secondary adrenal insufficiency, since 250 mcg is a supraphysiologic dose that can stimulate partially atrophied adrenals and produce a falsely reassuring result. A 2013 meta-analysis in the Journal of Clinical Endocrinology & Metabolism found that the low-dose test had superior sensitivity (92% vs. 64%) for secondary insufficiency, but at the cost of more complex preparation and higher variability in cortisol assay performance 6. Most centers still default to the 250 mcg protocol for practical reasons, reserving the low-dose test for cases where secondary insufficiency remains strongly suspected despite a normal standard-dose result.

The cosyntropin test does not reliably detect secondary adrenal insufficiency that developed within the prior 4 to 6 weeks, because the adrenal cortex has not yet had time to atrophy. In acute pituitary injury (surgery, apoplexy, traumatic brain injury), rely on the AM cortisol and ACTH levels rather than stimulation testing.

The Dexamethasone Suppression Test and Urinary Free Cortisol

When the AM cortisol is elevated and the clinical picture suggests Cushing syndrome (central obesity, proximal muscle wasting, violaceous striae wider than 1 cm, easy bruising, new-onset hypertension), confirmation requires at least two of three screening tests recommended by the Endocrine Society's 2008 guideline 4.

1 mg overnight dexamethasone suppression test (DST). The patient takes 1 mg of dexamethasone at 11:00 p.m. and has a serum cortisol drawn at 8:00 a.m. the next morning. A suppressed cortisol below 1.8 mcg/dL effectively rules out Cushing syndrome (sensitivity 95% or greater). Values above 1.8 mcg/dL require further testing. False positives occur with alcohol use disorder, depression, obesity, and medications that accelerate dexamethasone metabolism (phenytoin, carbamazepine, rifampin) through CYP3A4 induction 4.

24-hour urinary free cortisol (UFC). This test integrates cortisol production over a full day, bypassing the CBG-binding issue that confounds serum total cortisol. Values more than three-fold above the upper limit of normal are highly specific for Cushing syndrome. A single normal UFC does not exclude the diagnosis; the Endocrine Society recommends collecting at least two 24-hour samples because of episodic hypercortisolism in some patients 4.

Late-night salivary cortisol. Two collections on separate nights provide a combined sensitivity of 92 to 100% for Cushing syndrome 7. The patient collects saliva between 11:00 p.m. and midnight using a commercial collection device. Because salivary cortisol reflects the free fraction, it is unaffected by CBG changes.

Dr. Lynnette Nieman, a senior investigator at the National Institutes of Health and lead author of the Endocrine Society's Cushing guideline, has stated: "No single test is sufficient to diagnose Cushing syndrome. The combination of at least two concordant abnormal screening tests is required before proceeding to differential diagnosis" 4.

Renin, Aldosterone, and the Mineralocorticoid Axis

Cortisol is produced in the zona fasciculata, but the adrenal cortex has three functional zones. When evaluating adrenal disease, ignoring the mineralocorticoid axis (zona glomerulosa) can lead to missed diagnoses.

In primary adrenal insufficiency, aldosterone production fails alongside cortisol. Patients present with hyperkalemia, hyponatremia, and salt craving. A plasma renin activity (PRA) and serum aldosterone drawn simultaneously with the AM cortisol can confirm mineralocorticoid deficiency. An elevated PRA with low aldosterone is the expected pattern. This distinction matters for treatment: primary adrenal insufficiency requires fludrocortisone replacement in addition to hydrocortisone, while secondary insufficiency (where aldosterone is preserved because it is regulated primarily by the renin-angiotensin system, not ACTH) does not 2.

Separately, if hypertension and hypokalemia accompany an elevated cortisol, an aldosterone-to-renin ratio (ARR) screens for primary aldosteronism, which has a prevalence of 5 to 10% in hypertensive populations according to Endocrine Society estimates 8. The ARR is best drawn under standardized conditions: morning, seated for 15 minutes, with potassium repleted and interfering medications (spironolactone, eplerenone, amiloride) held for at least 4 weeks.

Thyroid and Metabolic Panel: Rounding Out the Picture

Adrenal insufficiency and hypothyroidism share symptoms (fatigue, weight gain, cold intolerance, cognitive slowing), and the two conditions can coexist in autoimmune polyglandular syndromes (APS). Type 2 APS pairs autoimmune adrenal insufficiency with autoimmune thyroid disease in roughly 50% of cases 9.

Adding a TSH and free T4 to an AM cortisol panel costs little and can prevent a diagnostic blind spot. There is also a physiologic interaction: cortisol is required for normal TSH suppression and peripheral T4-to-T3 conversion. Starting levothyroxine in a patient with undiagnosed adrenal insufficiency can precipitate an adrenal crisis by increasing metabolic clearance of cortisol. The standard of care is to confirm adrenal sufficiency and initiate glucocorticoid replacement before starting thyroid hormone replacement when both deficiencies are suspected 2.

A basic metabolic panel (BMP) also provides supporting data. Hyponatremia (from impaired free water excretion), hyperkalemia (from aldosterone deficiency), and hypoglycemia (from impaired gluconeogenesis) are classic laboratory features of adrenal insufficiency. In a patient with a borderline AM cortisol, these electrolyte abnormalities raise pre-test probability and argue for proceeding directly to stimulation testing.

How to Lower Elevated AM Cortisol

For patients with pathologically elevated AM cortisol from confirmed Cushing syndrome, treatment depends on the source. Transsphenoidal surgery remains first-line for pituitary adenomas, with initial remission rates of 65 to 90% at high-volume centers 10. Adrenal adenomas are treated with unilateral adrenalectomy. For patients who are not surgical candidates, medications such as ketoconazole (200 to 400 mg twice daily), osilodrostat (FDA-approved 2020, starting dose 2 mg twice daily), or pasireotide (0.6 to 0.9 mg subcutaneously twice daily) can reduce cortisol production 10.

For patients with mildly elevated AM cortisol that does not meet criteria for Cushing syndrome (functional or "stress-related" hypercortisolism), evidence supports behavioral interventions. A 2013 randomized trial (N=57) published in Health Psychology found that an 8-week mindfulness-based stress reduction (MBSR) program reduced salivary cortisol by 12% compared with controls 11. Sleep optimization, regular moderate-intensity aerobic exercise (150 minutes per week per ACSM guidelines), and cognitive behavioral therapy for chronic stress have shown cortisol-lowering effects in smaller studies, though effect sizes are modest and highly variable.

Dr. Maria Fleseriu, professor of medicine at Oregon Health & Science University and director of the Northwest Pituitary Center, has noted: "The distinction between pathologic hypercortisolism and physiologic stress responses is one of the most challenging diagnostic problems in endocrinology. Overreliance on a single AM cortisol without confirmatory testing leads to both over-diagnosis and missed diagnoses" 10.

How to Raise a Low AM Cortisol

If stimulation testing confirms adrenal insufficiency, glucocorticoid replacement is the treatment. The Endocrine Society recommends hydrocortisone 15 to 25 mg per day in two or three divided doses (the largest dose given on waking to mimic circadian physiology), or an equivalent dose of prednisone (3 to 5 mg daily) or modified-release hydrocortisone where available 2.

For secondary adrenal insufficiency caused by exogenous glucocorticoid withdrawal, a slow taper with periodic reassessment of the AM cortisol is standard. Most patients recover HPA axis function within 6 to 12 months, but some require up to 18 months. Recovery is tracked by checking an AM cortisol after holding the replacement dose for 24 hours; a value above 10 mcg/dL suggests the axis is recovering, and a cosyntropin stimulation test can confirm full recovery.

Patients with confirmed adrenal insufficiency must carry medical alert identification and have an emergency injection kit (dexamethasone 4 mg or hydrocortisone 100 mg intramuscular). Sick-day rules require doubling the oral glucocorticoid dose during febrile illness, and administering stress-dose hydrocortisone (50 to 100 mg IV/IM every 8 hours) during surgery, trauma, or hemodynamic instability 2.

Putting the Panel Together: A Decision Framework

The tests you order alongside an AM cortisol depend on the clinical question. A practical ordering framework:

Suspicion of adrenal insufficiency (fatigue, weight loss, hypotension, hyperpigmentation): AM cortisol + simultaneous ACTH + DHEA-S + BMP + renin + aldosterone. If AM cortisol is 3 to 15 mcg/dL, proceed to 250 mcg cosyntropin stimulation test. Add 21-hydroxylase antibodies if primary insufficiency is confirmed and autoimmune etiology is suspected.

Suspicion of Cushing syndrome (central obesity, striae, proximal weakness, new hypertension): AM cortisol + 1 mg overnight DST + 24-hour UFC (two collections) + two late-night salivary cortisols. If two of three screening tests are abnormal, add plasma ACTH for localization, then high-dose DST or inferior petrosal sinus sampling as directed by endocrinology.

Nonspecific fatigue with borderline cortisol: AM cortisol + ACTH + TSH + free T4 + BMP + CBC. Rule out thyroid dysfunction, anemia, and electrolyte abnormalities before attributing symptoms to adrenal disease.

Known autoimmune disease with new fatigue: AM cortisol + ACTH + DHEA-S + TSH + free T4 + fasting glucose. Screen for autoimmune polyglandular syndrome.