What is the normal 8am cortisol level?

From the Guidelines

A normal 8am cortisol level is less than 1.8 μg/dL (50 nmol/L) after a 1-mg dexamethasone suppression test, as indicated by the most recent and highest quality study 1. This morning measurement is crucial because cortisol follows a diurnal rhythm, with levels highest in the early morning and lowest around midnight. The 8am timing captures the peak of this natural cycle, providing the most reliable baseline assessment of adrenal function.

• Cortisol is a stress hormone produced by the adrenal glands that helps regulate metabolism, immune response, and blood pressure.
• Values below the normal range may suggest adrenal insufficiency, while consistently elevated levels could indicate conditions like Cushing's syndrome or chronic stress.
• It's essential to note that the normal range for 8am cortisol levels can vary depending on the specific test and laboratory, but the study 1 provides a clear guideline for interpretation after a dexamethasone suppression test.
• Another study 1 discusses various diagnostic tests for Cushing's syndrome, including the low-dose dexamethasone suppression test, but it does not provide a specific normal range for 8am cortisol levels.
• However, the most recent and highest quality study 1 takes precedence in guiding clinical decision-making, and its recommendation for a normal 8am cortisol level after a dexamethasone suppression test should be followed.

From the Research

Normal Cortisol Levels

• The normal 8am cortisol level is between 200-650 nmol/L 2
• After a low-dose dexamethasone test, the morning cortisol level is suppressed to <80 nmol/L in normal individuals 2
• Salivary cortisol concentration is an excellent indicator of plasma free cortisol concentration, with a normal range of 10.2-27.3 nmol/L at 0800 h 3

Cortisol Measurement

• Salivary cortisol measurements are a practical approach to assess pituitary-adrenal function 3
• 24-hour urinary free cortisol (UFC) excretion is also used to monitor cortisol levels, with normal values ranging from 10-65 μg/24 h 4
• Plasma cortisol levels can be measured, with a normal range of 150-300 nmol/L for the mean serum cortisol "day-curve" (CDC) 5

Factors Affecting Cortisol Levels

• Cortisol levels can be affected by various factors, including time of day, dexamethasone administration, and adrenal insufficiency 2, 3
• Elevated corticotropin concentrations (>300 pg/ml) can indicate primary adrenal insufficiency when cortisol levels are below 140 nmol/l (5 μg/dl) 6