What is the workup for hypercortisolism?

Workup for Hypercortisolism

The workup for hypercortisolism requires first confirming the diagnosis using at least two of three screening tests—24-hour urinary free cortisol (UFC), late-night salivary cortisol (LNSC), and low-dose dexamethasone suppression test (DST)—followed by plasma ACTH measurement to determine etiology, then imaging and potentially bilateral inferior petrosal sinus sampling (BIPSS) to localize the source. 1, 2

Step 1: Exclude Exogenous Glucocorticoid Use

• Before any biochemical testing, rule out iatrogenic Cushing's syndrome from exogenous glucocorticoid administration, as this is a common cause that requires no further workup 1, 2, 3

Step 2: Confirm Hypercortisolism with Initial Screening Tests

Use at least two of the following three tests to confirm the diagnosis (no single test has 100% diagnostic accuracy): 4, 1

24-Hour Urinary Free Cortisol (UFC)

• Collect at least 2-3 separate 24-hour urine samples to account for day-to-day variability (can be as high as 50%) 4, 5
• Diagnostic cutoff: >193 nmol/24h (>70 μg/m²) with 89% sensitivity and 100% specificity in children 4
• Advantage: Independent of corticosteroid-binding globulin (CBG) changes and dexamethasone compliance 4
• Limitations: Less reliable in renal impairment (CrCl <60 mL/min) or significant polyuria (>5 L/24h); influenced by sex, BMI, age, and sodium intake 4

Late-Night Salivary Cortisol (LNSC)

• Collect multiple samples at 11 PM (2300h) using commercial collection devices 6
• Sensitivity of 95-100% when using local assay-specific cutoffs 4, 6
• Advantage: Simple, non-invasive, reflects free (active) cortisol, useful for detecting intermittent hypercortisolism 6
• Preferred for shift workers or those with disrupted circadian rhythm 2

Low-Dose Dexamethasone Suppression Test (DST)

• Overnight 1 mg test: Give 1 mg dexamethasone at midnight, measure serum cortisol at 9 AM 1, 3
  • Normal suppression: cortisol <50 nmol/L (<1.8 μg/dL) 4
  • Cushing's syndrome: cortisol ≥50 nmol/L (≥1.8 μg/dL) with 95% sensitivity and 80% specificity 4
• Alternative 48-hour low-dose test: 0.5 mg every 6 hours for 48 hours (or 30 μg/kg/day in patients <40 kg) 4
• Measure dexamethasone levels concurrently to rule out abnormal metabolism and reduce false positives 4, 1
• Avoid in patients on estrogen-containing medications (causes false positives due to elevated CBG) 2

Midnight Serum Cortisol (Alternative)

• Measure sleeping midnight serum cortisol 4
• Diagnostic cutoff: ≥50 nmol/L (≥1.8 μg/dL) with 100% sensitivity but only 60% specificity 4

Step 3: Exclude Pseudo-Cushing's States

If screening tests are mildly abnormal, consider non-neoplastic hypercortisolism (pseudo-Cushing's) caused by: 4, 1, 2

• Severe obesity, uncontrolled diabetes, pregnancy
• Psychiatric disorders (especially depression)
• Alcohol use disorder
• Polycystic ovary syndrome
• Chronic kidney disease

Key distinguishing features: 4

• Pseudo-Cushing's typically shows UFC <3-fold above normal
• Consider Dex-CRH test or desmopressin test to differentiate true Cushing's from pseudo-Cushing's (both show good diagnostic performance) 4

Step 4: Determine Etiology with Plasma ACTH

Once hypercortisolism is confirmed, measure 9 AM plasma ACTH to differentiate ACTH-dependent from ACTH-independent causes: 4, 1, 2

ACTH-Dependent Cushing's (Normal or Elevated ACTH)

• ACTH >5 ng/L (>1.1 pmol/L) suggests pituitary or ectopic ACTH source 4, 1
• 68% sensitivity, 100% specificity for Cushing's disease 4

ACTH-Independent Cushing's (Low or Undetectable ACTH)

• Indicates primary adrenal source (adenoma, carcinoma, or bilateral hyperplasia) 1, 7
• Proceed directly to adrenal CT or MRI 1, 2, 7

Step 5: Localize the Source

For ACTH-Dependent Disease (Pituitary vs. Ectopic):

Pituitary MRI with contrast 4, 1, 2

• 63% sensitivity, 92% specificity for adenoma detection in children 4
• Microadenomas (<10 mm) are most common, especially in children (98% of cases) 4

If MRI is negative or equivocal, perform CRH stimulation test: 4, 1

• Give 1.0 μg/kg CRH intravenously 4
• Pituitary source: cortisol increase ≥20% (or ACTH increase ≥35%) with 74-100% sensitivity 4

Bilateral Inferior Petrosal Sinus Sampling (BIPSS) is the gold standard when MRI is negative/equivocal: 1, 2

• Must be performed when patient is hypercortisolemic to avoid false negatives 1
• Give CRH or desmopressin during sampling 4, 1
• Central-to-peripheral ACTH ratio ≥2 at baseline or ≥3 after stimulation confirms pituitary source with 100% sensitivity 4, 1
• Measure prolactin simultaneously to improve diagnostic accuracy 1
• Should be performed at specialized centers due to technical complexity and patient risks 1

For ACTH-Independent Disease (Adrenal Source):

Adrenal CT or MRI to identify: 1, 2, 7

• Adrenal adenoma (most common)
• Adrenal carcinoma
• Bilateral adrenal hyperplasia (micronodular or macronodular disease)
• MRI correctly diagnosed adenoma in 83% of cases in one surgical series 7

Special Populations and Considerations

Children and Adolescents

• Screen only if unexplained weight gain PLUS either decreased height velocity or declining height SD score (high sensitivity and specificity) 4
• Growth failure reliably distinguishes Cushing's from simple obesity in prepubertal children only 4
• Post-pubertal children should be assessed using adult guidelines 4
• Refer to multidisciplinary centers with pediatric endocrinology expertise 2
• Consider genetic testing, especially in young patients 2

Cyclic Cushing's Syndrome

• Can produce inconsistent results requiring periodic re-evaluation 1
• Late-night salivary cortisol measurements may be particularly useful for detecting intermittent hypercortisolism 6

Common Pitfalls to Avoid

• Never rely on a single test for diagnosis—false positives and negatives occur with all tests 4, 1
• Do not proceed directly to imaging without biochemical confirmation and ACTH determination (leads to incidental findings and misdiagnosis) 1
• Account for medications affecting dexamethasone metabolism: CYP3A4 inducers (phenobarbital, carbamazepine, St. John's wort) cause false positives; inhibitors (fluoxetine, cimetidine, diltiazem) cause false negatives 4
• Consider clinical context: severe depression, alcoholism, and severe obesity can all cause mild hypercortisolism mimicking Cushing's syndrome 4, 1