What is the interpretation of a three-sample saliva cortisol test for diagnosing adrenal insufficiency (Cortisol deficiency)?

From the Guidelines

A three-sample saliva cortisol test should be interpreted with caution, as the evidence demonstrating its benefit over serum cortisol is limited, and its practicality and feasibility are questionable 1. When interpreting the results of a three-sample saliva cortisol test, it is essential to examine the pattern of cortisol levels throughout the day to assess adrenal function. Normally, cortisol follows a diurnal rhythm with highest levels in the morning, a moderate decrease by midday, and lowest levels in the evening.

• Abnormal patterns include flat curves, suggesting adrenal fatigue or dysfunction
• Consistently high levels, possibly indicating chronic stress or Cushing's syndrome
• Consistently low levels, potentially signaling adrenal insufficiency or Addison's disease The timing of sample collection is crucial for accurate interpretation, typically upon waking, midday, and evening before bed.
• Factors that can affect results include acute stress, medications (particularly steroids), sleep quality, and food intake before testing
• If results are abnormal, follow-up testing such as an ACTH stimulation test or blood cortisol measurements may be needed, as recommended by recent guidelines 1 Understanding these patterns helps identify stress-related disorders, adrenal dysfunction, or other hormonal imbalances that might require lifestyle modifications or medical treatment.
• It is also important to consider the relationship between ACTH and cortisol to distinguish between primary and secondary adrenal insufficiency, as well as the potential impact of corticosteroid use on adrenal function 1
• Education on stress dosing, emergency injectables, and medical alert bracelets is crucial for patients with adrenal insufficiency, and endocrine consultation should be considered for planning and management 1

From the Research

Interpretation of Three-Sample Saliva Cortisol Test

The three-sample saliva cortisol test is used to diagnose adrenal insufficiency (cortisol deficiency) by measuring the levels of cortisol in saliva at different times of the day.

• The test typically involves collecting saliva samples at 8:00 am, 12:00 pm, and 4:00 pm, or at 8:00 am, 12:00 am (midnight), and 8:00 am after a dexamethasone suppression test (DST) 2, 3, 4.
• The normal range for salivary cortisol levels varies depending on the time of day and the laboratory methods used, but generally, morning levels are higher than evening levels 4, 5.
• A study found that a morning basal salivary cortisol level of less than 3.2 nmol/L had a sensitivity of 84.9% and specificity of 73.5% for diagnosing adrenal insufficiency 6.
• Another study found that a stimulated salivary cortisol level of less than 13.2 nmol/L had a sensitivity of 90.7% and specificity of 94.1% for diagnosing adrenal insufficiency 6.
• The diagnostic performance of stimulated salivary cortisol measurements after the short Synacthen test (SST) was comparable to serum cortisol measurements for diagnosing adrenal insufficiency 6.

Diagnostic Criteria

The diagnostic criteria for adrenal insufficiency using the three-sample saliva cortisol test are not strictly defined, but the following criteria have been suggested:

• A morning basal salivary cortisol level of less than 3.2 nmol/L 6
• A stimulated salivary cortisol level of less than 13.2 nmol/L after the SST 6
• A salivary cortisol level of less than 2.65 ng/ml at 8:00 am 3

Limitations

The three-sample saliva cortisol test has some limitations, including:

• Variability in salivary cortisol levels due to factors such as time of day, food intake, and stress 4, 5
• Limited standardization of laboratory methods for measuring salivary cortisol 2
• Potential for false-negative results in patients with mild adrenal insufficiency 6