What is the best time to check cortisol levels?

From the Guidelines

The best time to check cortisol levels is in the early morning, typically between 7 and 9 AM, when cortisol naturally reaches its peak in the body. This timing is crucial because cortisol follows a diurnal rhythm, with highest levels in the morning and lowest levels at night. For standard cortisol testing, patients should have their blood drawn in the morning while fasting.

Key Considerations

• If a more comprehensive assessment is needed, a 24-hour urine collection or salivary cortisol test may be recommended, which captures cortisol fluctuations throughout the day.
• For suspected adrenal disorders like Cushing's syndrome, late-night salivary cortisol (around 11 PM) may be ordered to check if levels remain inappropriately elevated when they should be at their lowest.
• Certain medications like steroids, estrogens, and some seizure medications can affect results, so these should be discussed with your healthcare provider before testing.
• Stress, illness, and strenuous exercise can temporarily increase cortisol levels, so it's best to be in a relaxed state when providing samples for the most accurate results.

Testing Protocols

• A 1 mg dexamethasone suppression test (DST) is often used to screen for autonomous cortisol secretion, with a serum cortisol level < 50 nmol/L at 8 AM indicating normal response 1.
• For patients with hypertension and/or hypokalemia, the aldosterone/renin ratio (ARR) is the preferred initial test, best done in the morning after the patient has been out of bed for 2 hours and seated for 5-15 minutes 1.

Evidence-Based Recommendations

• The most recent and highest quality study recommends checking cortisol levels in the morning, with a strong recommendation for the 1 mg DST as the preferred screening test for identifying autonomous cortisol secretion 1.
• Other studies support the use of late-night salivary cortisol testing for suspected Cushing's syndrome, with a sensitivity of 95% and specificity of 100% 1.

From the FDA Drug Label

1. 2 Single-Dose Short Test- Recommended Dose and Interpretation ... The blood sample for the assay is taken early the following morning (7:30-8:00 a.m.)

• The best time to check cortisol levels is early in the morning, specifically between 7:30-8:00 a.m., after administering metyrapone at midnight 2.
• This timing is based on the recommended dose and interpretation of the single-dose short test for diagnosing adrenal insufficiency.

From the Research

Best Time to Check Cortisol Levels

The best time to check cortisol levels can vary depending on the purpose of the test and the individual's circumstances. Here are some key points to consider:

• Cortisol levels typically follow a circadian rhythm, with peak levels in the morning and decreasing levels throughout the day 3.
• Studies have shown that midnight plasma cortisol levels can be an efficient and simple additional procedure for the diagnosis of Cushing's syndrome 4.
• Salivary cortisol levels can be measured at various times of the day, but late-night measurements may be useful for screening for Cushing's syndrome 5.
• The adrenocorticotropin stimulation test can be performed at different times of the day, but the 30-min cortisol response to ACTH is constant and unrelated to basal cortisol level or time of day 6.
• Morningness-eveningness can affect early-morning salivary cortisol levels, with morning types tend to have higher cortisol levels than evening types 7.

Key Findings

• Cortisol levels peak in the morning, typically around 07:48 h 3.
• Midnight plasma cortisol levels can be used to diagnose Cushing's syndrome 4.
• Salivary cortisol levels can be measured at late-night to screen for Cushing's syndrome 5.
• The 30-min cortisol response to ACTH is a reliable measure of adrenal response, regardless of time of day 6.
• Morningness-eveningness can influence early-morning salivary cortisol levels 7.

Considerations

• The purpose of the test and the individual's circumstances should be taken into account when determining the best time to check cortisol levels.
• Different methods of measuring cortisol levels, such as plasma, saliva, or urine, may have different optimal testing times 5.
• Individual variability in cortisol secretion patterns should be considered when interpreting test results 3.