From the Guidelines
Morning cortisol levels are considered normal when they are less than 1.8 μg/dL (50 nmol/L) after a 1-mg dexamethasone suppression test. This is based on the most recent and highest quality study available, which was published in 2021 in The Lancet Diabetes and Endocrinology 1.
Key Points to Consider
- The dexamethasone suppression test is used to assess cortisol production and diagnose conditions such as Cushing's syndrome.
- A serum cortisol level of less than 1.8 μg/dL (50 nmol/L) at 0800 h in the morning after 1 mg dexamethasine given between 2300 h and midnight is considered a normal response.
- Factors such as rapid absorption or malabsorption of dexamethasone, concomitant treatment with CYP3A4 inducers, and increased corticosteroid binding globulin (CBG) levels can lead to false positive results.
- Measuring dexamethasone concomitantly with cortisol and using laboratory-specific ranges of expected values can reduce the risk of false-positive results.
- False negative results are less common, but can occur due to inhibition of dexamethasone metabolism by concomitant medications or decreased CBG and albumin levels.
Clinical Implications
- Morning cortisol levels should be interpreted in the context of the dexamethasone suppression test to accurately diagnose and manage conditions such as Cushing's syndrome.
- Clinicians should be aware of the potential factors that can affect cortisol levels and take them into account when interpreting test results.
- The use of laboratory-specific ranges of expected values and measurement of dexamethasone concomitantly with cortisol can help improve the accuracy of test results.
From the Research
Normal Morning Cortisol Levels
The normal morning cortisol level can vary depending on several factors, including the individual's health status and the laboratory methods used to measure cortisol.
- According to the study 2, basal cortisol levels in normal subjects were not explicitly stated, but the study compared cortisol levels in patients with systemic lupus erythematosus to those in normal subjects.
- The study 3 presented a method for quantifying cortisol in serum, ultrafiltrate, and saliva, but did not provide specific values for normal morning cortisol levels.
- The study 4 discussed the dexamethasone suppression test and its ability to predict impaired adrenal function after prednisone treatment, but did not provide specific values for normal morning cortisol levels.
- The study 5 developed a method for quantifying unbound prednisolone, prednisone, cortisol, and cortisone in human plasma, but did not provide specific values for normal morning cortisol levels.
- The study 6 presented a method for simultaneously determining plasma prednisolone, prednisone, and cortisol levels, but did not provide specific values for normal morning cortisol levels.
Cortisol Measurement
Cortisol levels can be measured in various biological samples, including serum, ultrafiltrate, and saliva.
- The study 3 found that salivary levels of cortisol correlated well with ultrafiltrate levels.
- The study 5 developed a method for quantifying unbound cortisol in human plasma using ultrafiltration and liquid chromatography-tandem mass spectrometry.
- The study 6 presented a method for simultaneously determining plasma prednisolone, prednisone, and cortisol levels using high-performance liquid chromatography.