What cortisol levels are considered high for a 3-sample night time saliva cortisol test?

From the Guidelines

For a 3-sample nighttime saliva cortisol test, levels above 0.35-0.40 μg/dL (or 9.7-11.0 nmol/L) are generally considered high. When interpreting the results of a 3-sample nighttime saliva cortisol test, it is essential to consider the normal circadian rhythm of cortisol secretion, which typically reaches its nadir between 11 PM and midnight, ranging from 0.05-0.35 μg/dL 1. Elevated nighttime cortisol levels may indicate disruption of this normal diurnal pattern, a hallmark of conditions like Cushing's syndrome.

Key Considerations

• Normal nighttime cortisol levels should be at their lowest between 11 PM and midnight, ranging from 0.05-0.35 μg/dL as part of the body's natural circadian rhythm.
• Elevated nighttime cortisol is significant because it may indicate disruption of the normal diurnal pattern.
• When interpreting results, it's crucial to consider that cortisol levels can be temporarily elevated due to stress, intense exercise, certain medications (including oral contraceptives, estrogen, and glucocorticoids), or eating shortly before the test 1.
• For accurate results, samples should be collected at the recommended times (usually late evening), and patients should avoid brushing teeth, eating, drinking anything besides water, or using tobacco products for at least 30 minutes before collection.
• Multiple samples help establish a pattern rather than relying on a single measurement, providing more reliable diagnostic information.

Clinical Recommendations

• The diagnostic utility of late-night saliva cortisol (LNSC) tests is based on the assumption that patients with Cushing's syndrome (CS) lose the normal circadian nadir of cortisol secretion 1.
• At least two or three LNSC tests are recommended for diagnostic purposes.
• Patients with mild CS may have LNSC just above the upper limit of normal (ULN).
• Sampling saliva at usual bedtime rather than at midnight could decrease false positive results, as cortisol nadir is tightly entrained to sleep onset 1.

From the Research

Cortisol Levels in 3-Sample Night Time Saliva Test

The following parameters are considered high for a 3-sample night time saliva cortisol test:

• A 2300-h salivary cortisol level greater than 3.6 nmol/L 2
• An assay-specific inpatient 2400-h salivary cortisol or an outpatient bedtime salivary cortisol greater than 550 ng/dl (15.2 nmol/liter) 3
• A cut-off point of 1.9 nmol/l for salivary cortisol measurement in the overnight 1-mg dexamethasone suppression test 4
• A cut-off value of 0.18 μg/dL for late-night salivary cortisol in diagnosing subclinical Cushing's syndrome 5

Key Findings

• Late-night salivary cortisol measurement is a simple and reliable screening test for spontaneous Cushing's syndrome 2, 6
• Salivary cortisol measurements work as well as plasma measurements and better than urine glucocorticoid excretion in diagnosing Cushing's syndrome 3
• The sensitivity and specificity of late-night salivary cortisol for diagnosing subclinical Cushing's syndrome are limited, and it should be used as an adjunct test to other tests 5

Diagnostic Value

• The diagnostic value of late-night salivary cortisol for diagnosis of subclinical Cushing's syndrome is somewhat controversial 5
• Late-night salivary cortisol can be used as a screening test for Cushing's syndrome, but it should be interpreted with caution and in combination with other diagnostic tests 2, 6, 3, 4