Cortisol Level Interpretation Guidelines

Diagnostic Thresholds for Adrenal Insufficiency and Cushing's Syndrome

A morning serum cortisol level <275 nmol/L (<10 μg/dL) is concerning and warrants further investigation with ACTH stimulation testing, according to the Endocrine Society 1, 2
The Endocrine Society recommends that a post-dexamethasone suppression test cortisol level >50 nmol/L (>1.8 μg/dL) is concerning for Cushing's syndrome 1, 2
A peak cortisol level <500 nmol/L (<18 μg/dL) after ACTH stimulation is diagnostic of adrenal insufficiency, as stated by the American Association of Clinical Endocrinologists 1, 3, 4
The American College of Endocrinology suggests that a peak cortisol level >550 nmol/L (>20 μg/dL) after ACTH stimulation is considered normal 4

A post-dexamethasone suppression test cortisol level >138 nmol/L (>5 μg/dL) is highly suggestive of autonomous cortisol production from an adrenal incidentaloma with overt Cushing's syndrome, according to the Endocrine Society 1
Late-night salivary cortisol values above the upper limit of normal indicate loss of normal circadian rhythm and are concerning for Cushing's syndrome; at least 2-3 tests are recommended by the American Association of Clinical Endocrinologists 1, 2
The European Society of Endocrinology states that 24-hour urinary free cortisol values above the upper limit of normal on 2-3 collections suggest Cushing's syndrome, though this test has the lowest sensitivity among screening tests 1, 2
A midnight serum cortisol level ≥50 nmol/L (≥1.8 μg/dL) has 100% sensitivity for Cushing's syndrome in children and young people, as reported by the Pediatric Endocrine Society 3

The American College of Emergency Physicians recommends that if a patient presents with unexplained hypotension, collapse, or gastrointestinal symptoms, immediately administer IV hydrocortisone 100 mg and 0.9% saline infusion without waiting for cortisol results 4
Hyponatremia is present in 90% of newly diagnosed adrenal insufficiency cases, but absence of hyperkalemia cannot rule out the diagnosis, according to the National Institute of Diabetes and Digestive and Kidney Diseases 4
Increased cortisol-binding globulin from oral estrogens, pregnancy, or chronic hepatitis falsely elevates total serum cortisol, as stated by the Endocrine Society 1
Decreased cortisol-binding globulin from nephrotic syndrome or malnutrition falsely lowers total serum cortisol, according to the American Journal of Kidney Diseases 1
CYP3A4 inducers accelerate dexamethasone metabolism, causing false-positive suppression tests, as reported by the European Society of Endocrinology 1
Exogenous steroids including inhaled fluticasone can suppress the HPA axis and confound results, according to the American Thoracic Society 4

A random afternoon cortisol level ≥50 nmol/L (≥1.8 μg/dL) is concerning for Cushing's syndrome, particularly when measured at midnight or late evening, as this indicates loss of normal circadian rhythm 5, 6
Midnight serum cortisol ≥50 nmol/L (≥1.8 μg/dL) has 100% sensitivity for Cushing's syndrome in pediatric populations and demonstrates excellent diagnostic accuracy in adults 5, 6
Evening cortisol ≥50 nmol/L (≥1.8 μg/dL) in the context of suspected hypercortisolism warrants further investigation with formal screening tests 5
Post-dexamethasone PM cortisol >50 nmol/L (>1.8 μg/dL) is diagnostic of Cushing's syndrome 5, 6

If measured between 23:00-01:00h (midnight): Any value ≥50 nmol/L (≥1.8 μg/dL) is highly concerning and should prompt formal Cushing's screening 5, 6
The Endocrine Society recommends proceeding with formal Cushing's screening if midnight or late-night cortisol levels are elevated, which includes obtaining at least two of the following: 24-hour urinary free cortisol, late-night salivary cortisol on 2-3 occasions, or overnight 1-mg dexamethasone suppression test 5

Measure 09:00h plasma ACTH to differentiate ACTH-dependent from ACTH-independent causes once hypercortisolism is confirmed 5, 6
Recent exogenous steroid use can suppress or confound results; ensure 2-week washout period before interpretation 7

The normal circadian nadir should result in cortisol levels well below the threshold of 50 nmol/L in healthy individuals 8
Pregnancy and chronic active hepatitis increase cortisol-binding globulin (CBG) and total cortisol, which can affect cortisol level interpretation 8
Healthy individuals should have cortisol nadir tightly entrained to sleep onset, with levels dropping to <50 nmol/L by late evening 8

Night-shift workers should not use late-night cortisol testing due to disrupted circadian rhythm 8
Cyclic Cushing's syndrome may require multiple sequential late-night measurements over weeks to months to capture episodic cortisol excess 8

Elevated cortisol levels indicate potential pathologic hypercortisolism, requiring systematic diagnostic workup to identify the underlying cause and prevent serious morbidity, including cardiovascular disease, diabetes, osteoporosis, infections, and increased mortality, according to the Endocrine Society 9

The Endocrine Society recommends beginning with any of the following tests based on availability—no single test is preferred: dexamethasone suppression test, late-night salivary cortisol, 24-hour urinary free cortisol, or midnight serum cortisol 10
Depression, alcoholism, and severe obesity can cause physiologic hypercortisolism mimicking Cushing's syndrome, and management of pseudo-Cushing's involves monitoring for 3-6 months, treating the underlying condition, and repeating testing after 2-week washout from exogenous steroids or stopping oral contraceptives, as suggested by the Endocrine Society 10

Rapid normalization of cortisol is the primary goal to prevent life-threatening complications in severe hypercortisolism, and first-line medical therapy includes osilodrostat or metyrapone, according to the Endocrine Society 9
The Endocrine Society recommends ketoconazole, osilodrostat, or metyrapone for mild-to-moderate disease, and considers cabergoline or pasireotide for potential tumor shrinkage, although pasireotide has a high hyperglycemia risk 9

Post-treatment monitoring requires assessing for adrenal insufficiency symptoms and using multiple serial urinary free cortisol and late-night salivary cortisol tests to assess treatment response, as recommended by the Endocrine Society 9