How do I check my cortisol level?

How to Check Your Cortisol Level

The optimal method to check cortisol depends on your clinical scenario: for screening suspected adrenal insufficiency, obtain a morning (8:00-9:00 AM) serum cortisol; for screening suspected Cushing's syndrome, perform an overnight 1-mg dexamethasone suppression test with 8:00 AM cortisol measurement. 1, 2, 3

Timing is Critical for Accurate Testing

Always draw morning cortisol between 8:00-9:00 AM to capture the physiologic peak of cortisol secretion, which provides the most reliable assessment of adrenocortical function. 3 This timing is essential because:

• Cortisol follows a circadian rhythm with peak levels in early morning (140-700 nmol/L at 9:00 AM) and nadir at midnight (80-350 nmol/L). 3
• The same cortisol value may be normal at 9:00 AM but pathologically elevated at midnight, making timing interpretation critical. 3
• Never interpret a cortisol value without knowing the exact collection time. 3

Important Exceptions to Morning Testing

• Night-shift workers and patients with disrupted circadian rhythms should not undergo standard morning cortisol testing, as their cortisol peaks occur at different times and will yield unreliable results. 3
• For these patients, the dexamethasone suppression test is preferred over late-night salivary cortisol. 3

Sample Collection Methods

Serum Cortisol (Blood Test)

• Most common and widely available method using venipuncture at 8:00-9:00 AM. 1, 3
• Measures total cortisol (bound + free), which can be affected by conditions altering cortisol-binding globulin. 4, 5
• Results available same day in most laboratories. 4, 5

24-Hour Urinary Free Cortisol

• Requires complete 24-hour urine collection with measurement of volume and creatinine to verify completeness. 1
• At least 2-3 collections are recommended due to up to 50% random variability between collections. 1
• Normal values: <193 nmol/24h (<70 μg/m²/24h). 1
• Primarily used for Cushing's syndrome screening, not adrenal insufficiency. 1, 3

Late-Night Salivary Cortisol

• Collected at usual bedtime (typically 11:00 PM-midnight) using specialized collection devices. 1, 3
• Obtain 2-3 samples on different nights to account for variability. 1
• Reflects free (biologically active) cortisol and detects loss of normal circadian rhythm. 1, 4
• Abnormal threshold: >3.6 nmol/L with >90% sensitivity for Cushing's syndrome. 1

Clinical Scenarios and Testing Approach

Suspected Adrenal Insufficiency

Order morning (8:00-9:00 AM) serum cortisol as the initial test. 2, 3

Interpretation thresholds:

• <275 nmol/L (<10 μg/dL): Concerning, proceed to ACTH stimulation test. 2, 6
• <110 nmol/L: Highly suggestive of adrenal insufficiency. 7
• >300 nmol/L: Effectively excludes adrenal insufficiency in unstressed patients. 7
• Between 110-300 nmol/L: Perform ACTH stimulation test for definitive diagnosis. 7

Critical pitfall: If the 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. 2

Suspected Cushing's Syndrome

Perform overnight 1-mg dexamethasone suppression test as the preferred initial screening test. 3

Protocol:

• Administer 1 mg dexamethasone orally at 11:00 PM. 3
• Draw serum cortisol at 8:00 AM the following morning. 3

Interpretation:

• <50 nmol/L (<1.8 μg/dL): Excludes cortisol hypersecretion. 3
• 51-138 nmol/L (1.8-5 μg/dL): Suggests possible autonomous cortisol secretion. 3
• >138 nmol/L (>5 μg/dL): Evidence of cortisol hypersecretion/overt Cushing's syndrome. 1, 3

Complementary tests if initial screening is equivocal:

• Late-night salivary cortisol (2-3 samples). 1, 3
• 24-hour urinary free cortisol (2-3 collections). 1, 3

Critical Factors That Affect Results

Medications and Substances

• Oral contraceptives and estrogen therapy increase cortisol-binding globulin, falsely elevating total cortisol. 1, 2
• CYP3A4 inducers (phenytoin, rifampin, carbamazepine) accelerate dexamethasone metabolism, causing false-positive suppression tests. 1, 2
• Inhaled fluticasone can suppress the HPA axis and confound results. 1, 2
• Topical hydrocortisone can contaminate samples, especially salivary cortisol. 1

Physiologic States

• Pregnancy and chronic active hepatitis increase cortisol-binding globulin, elevating total cortisol. 1, 2
• Physical stress (strenuous exercise within 24-48 hours) elevates cortisol. 1
• Acute psychological stress increases cortisol secretion. 1
• Sleep disturbances affect morning awakening cortisol patterns. 1

Pseudo-Cushing's States

Psychiatric disorders, alcohol use disorder, polycystic ovary syndrome, and severe obesity can activate the HPA axis, causing mildly elevated cortisol that mimics true hypercortisolism. 1, 2

When to Measure ACTH Simultaneously

Always draw ACTH simultaneously with morning cortisol when evaluating adrenal insufficiency to distinguish primary from secondary causes. 3

Interpretation:

• High ACTH + low cortisol: Primary adrenal insufficiency (Addison's disease). 3
• Low ACTH + low cortisol: Secondary (central) adrenal insufficiency or glucocorticoid-induced suppression. 3

Critical handling requirement: ACTH is extremely labile and requires immediate processing on ice—coordinate with the laboratory before drawing. 3

Laboratory Methods

• Automated immunoassays are most widely used but lack specificity and show significant inter-assay differences. 4, 5
• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers improved specificity and sensitivity, particularly for salivary cortisol. 4, 5
• Reference ranges may vary between laboratories and assay methods—always use your laboratory's specific cutoffs. 4, 5