From the Guidelines
Normal cortisol levels are typically considered to be less than 1.8 μg/dL (50 nmol/L) at 0800 h in the morning after a 1-mg dexamethasone suppression test, as indicated by the most recent guideline update 1. This guideline update provides the most recent and highest quality evidence for determining normal cortisol levels.
- The normal response to the dexamethasone suppression test is a serum cortisol level of less than 1.8 μg/dL (50 nmol/L) at 0800 h in the morning, which strongly predicts the absence of Cushing's syndrome (CS) 1.
- It's essential to consider the timing of cortisol level testing, as cortisol secretion follows a natural circadian rhythm, with levels typically highest in the early morning and decreasing throughout the day 1.
- The hypothalamic-pituitary-adrenal (HPA) axis regulates cortisol production, and specialized tests like the ACTH stimulation test or overnight dexamethasone suppression test may be needed for accurate assessment of adrenal function 1.
- False positive or false negative results can occur due to various factors, such as rapid absorption or malabsorption of dexamethasone, concomitant treatment with certain medications, or changes in corticosteroid binding globulin (CBG) levels 1.
- Measuring dexamethasone concomitantly with cortisol and using laboratory-specific ranges of expected values can help reduce the risk of false-positive results 1.
From the Research
Normal Cortisol Levels
- The normal range for 24-hour urinary free cortisol (UFC) excretion is 10-65 μg/24 h, as stated in the study 2.
- This range is used as a reference to diagnose and monitor conditions such as Cushing's syndrome.
- It is essential to note that cortisol levels can vary depending on the individual and the testing method used.
Factors Affecting Cortisol Measurement
- Certain medications, such as ketoconazole and metyrapone, can alter the urinary excretion of steroid metabolites, affecting the reliability of urinary free cortisol immunoassay determinations 3.
- The use of these medications can lead to overestimation or underestimation of cortisol levels, making it crucial to consider these factors when interpreting test results.
Clinical Significance of Cortisol Levels
- Elevated cortisol levels can increase the risk of cardiovascular risk factors, cardiovascular events, metabolic bone disease, and mortality, as seen in patients with mild autonomous cortisol secretion (MACS) 4.
- Accurate measurement and interpretation of cortisol levels are vital for diagnosing and managing conditions related to cortisol imbalance.