What is the normal 8am cortisol level in micrograms per deciliter (mcg/dL)?

From the Guidelines

A normal 8am cortisol level is less than 1.8 μg/dL in healthy individuals after a 1-mg dexamethasone suppression test, as indicated by the most recent guideline update 1. This morning cortisol measurement is crucial because cortisol follows a diurnal pattern, with levels highest in the early morning and lowest around midnight.

Key Points to Consider

• The 8am timing is specifically chosen to capture the peak of this natural rhythm.
• Cortisol is a stress hormone produced by the adrenal glands that helps regulate metabolism, immune function, and stress response.
• Values below 1.8 μg/dL after the dexamethasone suppression test may suggest a normal response, while consistently elevated levels could indicate conditions like Cushing's syndrome or excessive stress.
• It's worth noting that cortisol levels can be affected by factors such as sleep patterns, stress, medications (particularly steroids), and the timing of blood collection, so these should be considered when interpreting results.
• For accurate assessment, patients should avoid unusual physical or emotional stress before testing and follow any specific preparation instructions provided by their healthcare provider.

Important Considerations

• False positive results may be seen with rapid absorption/malabsorption of dexamethasone due to increased gut transit time, chronic diarrhea, or celiac disease; concomitant treatment with CYP3A4 inducers (e.g., phenobarbital, carbamazepine, St. John’s wort); and increased corticosteroid binding globulin (CBG) levels from oral estrogens, pregnancy, or chronic active hepatitis, which may increase total cortisol levels 1.
• Measuring dexamethasone concomitantly with cortisol, using laboratory-specific ranges of expected values, can reduce the risk for false-positive results 1.

From the Research

Normal 8am Cortisol Levels

• The normal 8am cortisol level in micrograms per deciliter (mcg/dL) is not explicitly stated in the provided studies as a single definitive value.
• However, according to 2, a morning serum cortisol level >13 mcg/dL reliably rules out adrenal insufficiency.
• Study 3 suggests that morning cortisol concentrations of >350 nmol/l (approximately 12.6 mcg/dl) are considered to safely rule out Addison's disease, and values >500 nmol/l (approximately 18 mcg/dl) are recommended as a threshold for testing.
• In 4, a mean basal morning serum cortisol of > or = 300 nmol/L (approximately 10.9 mcg/dL) excluded the possibility of adrenal insufficiency.
• It is essential to note that cortisol levels can vary, and these values are used as guidelines for diagnosing adrenal insufficiency rather than defining a normal range for the general population 5, 4, 6.

Cortisol Level Variations

• The studies provided focus on the diagnosis of adrenal insufficiency and do not give a specific normal range for 8am cortisol levels in the general population.
• Cortisol levels can be influenced by various factors, including the time of day, with levels typically peaking in the morning and decreasing at night 5.
• The Elecsys Cortisol II assay used in 6 reports cortisol levels during the standard-dose cosyntropin stimulation test, with median levels of 21.7 µg/dl and 24.4 µg/dl at 30- and 60-minutes after cosyntropin administration, respectively. However, these values are not directly related to normal 8am cortisol levels.