What can falsely elevate morning (AM) cortisol levels?

False Elevation of Morning (AM) Cortisol Levels

The most common causes of falsely elevated morning cortisol are increased cortisol-binding globulin (CBG) from oral estrogen-containing medications (including oral contraceptives), pregnancy, and chronic active hepatitis, which elevate total cortisol while free (biologically active) cortisol remains normal. 1, 2

Primary Causes of False Elevation

Medications Increasing Cortisol-Binding Proteins

• Oral contraceptives and estrogen therapy are the most clinically significant causes of falsely elevated total cortisol, as estrogen increases CBG levels, which can raise total cortisol measurements dramatically while free cortisol remains normal. 1, 2, 3
• Modern oral contraceptives, even those with low to moderate estrogen content, can cause extreme increases in serum cortisol (documented cases showing levels rising from 10 mcg/dL to 50-61 mcg/dL) due to marked CBG elevation. 4
• Exogenous corticosteroids (oral prednisolone, dexamethasone, fluticasone inhalers) can confuse interpretation of serum cortisol levels through cross-reactivity in immunoassays or by suppressing endogenous production. 2, 5

Physiologic States Affecting CBG

• Pregnancy increases CBG levels, leading to elevated total cortisol measurements that do not reflect true hypercortisolism. 1, 3
• Chronic active hepatitis can increase CBG production, falsely elevating total cortisol. 1

Assay-Related Causes

Immunoassay Interference

• Heterophile antibodies and other interfering substances in the patient's serum can cause falsely low or high cortisol results depending on the specific immunoassay platform used. 6
• Automated immunoassays lack specificity and show significant inter-assay differences, with potential for cross-reactivity with other steroids or medications. 7
• Topical hydrocortisone preparations can contaminate samples and cause falsely elevated results, particularly in salivary cortisol measurements (though mass spectrometry can distinguish cortisol from cortisone to avoid this). 1

Sample Collection Issues

• Blood contamination from recent dental work, teeth brushing, or oral trauma within 1-2 hours of collection can lead to falsely elevated biomarker levels in salivary samples. 1
• Acute infection, especially upper respiratory tract infections, can elevate immune and related markers that may interfere with cortisol measurements. 1

Physiologic and Behavioral Factors

Stress and Activity

• Physical stressors including strenuous exercise within 24-48 hours before sampling can elevate cortisol levels. 1
• Mental and cognitive stressors, including stress from neurocognitive assessments, can acutely elevate cortisol and should be avoided before sampling. 1
• Acute psychological stress increases cortisol secretion, potentially causing transiently elevated morning values. 1

Circadian Rhythm Disruption

• Night-shift workers and those with disrupted sleep-wake cycles may have abnormal cortisol timing, making standard morning measurements unreliable. 1, 3
• Sleep disturbances can affect morning awakening cortisol patterns, though effects vary by population. 1

Pseudo-Cushing's States

• Psychiatric disorders, alcohol use disorder, polycystic ovary syndrome, and severe obesity can activate the hypothalamic-pituitary-adrenal axis, causing mildly elevated cortisol that mimics true hypercortisolism. 1, 2
• These conditions tend to produce only mildly elevated results rather than the marked elevations seen in true Cushing's syndrome. 1

Critical Pitfall to Avoid

• The most important clinical pitfall is interpreting elevated total cortisol as pathologic without considering CBG status—always inquire about oral contraceptives, estrogen therapy, and pregnancy before pursuing extensive workup for hypercortisolism. 1, 2, 4
• When elevated cortisol is suspected to be artifactual, measuring free cortisol (via 24-hour urinary free cortisol or salivary cortisol) or measuring CBG levels directly can clarify whether true hypercortisolism exists. 7
• Concomitant measurement of dexamethasone levels with cortisol during suppression testing can reduce false-positive results by confirming adequate drug absorption and metabolism. 1, 3