Night-Time Salivary Cortisol Testing for Diagnosing Cushing’s Disease

March 19, 2025

Night-time salivary cortisol testing is an essential, non-invasive tool that helps detect abnormalities in cortisol levels—particularly useful for diagnosing Cushing’s disease and evaluating diurnal rhythm disorders.

What Is Salivary Cortisol Testing?

Salivary testing is used to assess hormone levels aligned with your body’s circadian rhythm (also called diurnal rhythm). While many hormones don’t correlate well between blood and saliva, cortisol is an exception—saliva levels closely reflect blood levels.

In healthy individuals, cortisol peaks in the early morning, telling the body it’s time to wake up. Cortisol levels typically decline throughout the day, reaching their lowest at night.

Why Is Night-Time Cortisol Important in Cushing’s Disease?

In patients with Cushing’s disease, this natural rhythm is disrupted. Elevated night-time cortisol levels are a hallmark of the condition, keeping the body alert when it should be winding down for sleep.

This abnormal pattern is a key diagnostic clue. Night-time salivary cortisol testing provides a practical and reliable method for identifying this irregularity.

What Is Episodic Cushing’s Syndrome?

Cushing’s isn’t always consistent. Many patients have episodic or periodic Cushing’s, meaning cortisol levels spike unpredictably. Unlike “cyclic Cushing’s,” which implies regular patterns, episodic Cushing’s is harder to catch with a single test.

Dr. Friedman’s 2010 study published in Hormone and Metabolic Research found that 65 out of 66 patients with Cushing’s had at least one normal cortisol test—underscoring the need for multiple tests during “high” episodes.

How to Recognize a “High Cortisol” Episode

You should aim to test when you’re experiencing symptoms of a cortisol spike. Patients often describe:

• Wired energy late at night
• Rapid weight gain or water retention (edema)
• Acne or flushed skin
• Insomnia or restless sleep
• Mood swings, irritability, or euphoria
• Unusual energy surge after sunset
• Racing thoughts or fast speech
• High blood pressure or blood sugar
• Tasks feel easier, aches and pains diminish

Pro tip: Keep a symptom diary to help identify patterns and improve timing of your tests.

How to Collect Night-Time Saliva Samples

Collection protocols differ slightly between LabCorp and Quest Diagnostics. Always use the correct Salivette kit from the same lab where your test will be processed.

Preparation (for Both Labs)

• Avoid steroid creams/inhalers 24 hours before
• No food, drink, brushing, or flossing 30–60 minutes before
• Collect sample between 11 PM and 12:30 AM
• Label each sample with name, DOB, date, and time
• Store refrigerated or frozen as required

LabCorp Saliva Collection Steps

1. Use 4 white-top Salivettes
2. Roll cotton in mouth for 90+ seconds (until saturated)
3. Return to vial and seal
4. Refrigerate or freeze per instructions

Stability:

• Room Temp: 14 days
• Fridge: 14 days
• Frozen: 5 months

Quest Diagnostics Collection Steps

1. Use 4 blue-top Salivettes
2. Keep swab in cheek for 2+ minutes
3. Return swab and seal container
4. Refrigerate or freeze per instructions

Stability:

• Room Temp: 72 hours
• Fridge: 21 days
• Frozen: 6 months

Sample Drop-Off

Freeze all samples if needed and drop them off together at your lab’s local pickup station. If questioned, mention the lab’s own instructions allow for freezing.

When Will You Get Results?

Results are typically available 10–14 days after submission. Dr. Friedman will analyze your cortisol levels in relation to your symptoms and guide further testing or treatment.