What does a cortisol level of 22.2 at 10 am indicate?

Interpretation of Cortisol Level of 22.2 at 10 am

A cortisol level of 22.2 µg/dL at 10 am falls within the normal reference range and does not indicate pathology, as morning cortisol levels typically range from 8-25 µg/dL.

Normal Cortisol Physiology

Cortisol follows a diurnal pattern with highest levels in the early morning (typically 8-10 am) and lowest levels at night. According to diagnostic guidelines:

• Normal morning cortisol levels typically range from 8-25 µg/dL (220-690 nmol/L) 1
• Cortisol levels gradually decrease throughout the day
• A level of 22.2 µg/dL at 10 am is within the upper normal range

Diagnostic Considerations

When evaluating a single cortisol measurement, several important factors should be considered:

Measurement Method

• Immunoassays are commonly used but may lack specificity compared to LC-MS/MS 2, 3
• Different assays may have slightly different reference ranges
• Results should be interpreted based on the specific laboratory's reference range

Factors That Can Affect Cortisol Levels

• Stress can transiently elevate cortisol levels
• Medications, particularly estrogen-containing oral contraceptives, can significantly increase total serum cortisol by elevating cortisol-binding globulin (CBG) 4
• Time of day is critical for interpretation - a value of 22.2 would be abnormal at midnight but normal at 10 am

When Further Testing Is Warranted

A single cortisol measurement is rarely diagnostic. If there is clinical suspicion of adrenal dysfunction despite a normal morning cortisol:

For Suspected Cushing's Syndrome:

• 24-hour urinary free cortisol (UFC) measurement
• Late-night salivary cortisol test
• Overnight 1-mg dexamethasone suppression test (DST) 1

For Suspected Adrenal Insufficiency:

• ACTH stimulation test
• Morning ACTH level measurement

Clinical Context Matters

The clinical significance of a cortisol level of 22.2 µg/dL at 10 am depends on the patient's presentation:

• In an asymptomatic patient: This is a normal finding requiring no further workup
• In a patient with symptoms suggestive of cortisol excess: A normal morning cortisol does not rule out Cushing's syndrome, and further testing would be indicated
• In a patient with symptoms of adrenal insufficiency: This normal value makes primary adrenal insufficiency unlikely

Key Points to Remember

• A single cortisol measurement has limited diagnostic value
• The time of collection is critical for interpretation
• Clinical correlation is essential
• If adrenal pathology is suspected despite a normal morning cortisol, dynamic testing should be pursued
• Medications, particularly estrogen-containing contraceptives, can significantly affect total cortisol levels without affecting free cortisol 4

In summary, a cortisol level of 22.2 µg/dL at 10 am is within normal limits and, in isolation, does not suggest adrenal pathology.