When is nighttime cortisol test ordered And what are its implications

Do you suffer from sudden weight gain, high blood pressure, muscle weakness, or sleep disturbances?Your doctor may recommend a late-night cortisol test, one of the most important tests used to detect abnormal levels of the cortisol hormone, especially in suspected cases of Cushing's syndrome.In this article from    Dalili Medical, we guide you through everything you need to know about this crucial test — its purpose, how it's performed, normal reference values, and what the results may indicate.

What Is the Late-Night Cortisol Test?

The Late-Night Cortisol Test measures the level of cortisol, the body’s primary stress hormone, in either blood or saliva collected between 11 PM and 12 midnight—the time when cortisol should be at its lowest in healthy individuals.

If cortisol levels are abnormally high at night, it may indicate a dysfunction in the adrenal or pituitary glands.

Why Is the Late-Night Cortisol Test Important?

✅ It helps in:

• Diagnosing Cushing’s Syndrome (excess cortisol production)

• Evaluating adrenal gland disorders

• Ruling out psychological or medication-related causes of high cortisol

• Monitoring treatment progress in pituitary or adrenal tumors

What Is Cortisol?

Cortisol is a hormone produced by the adrenal cortex. It is often called the "stress hormone" because its levels increase in response to physical or emotional stress.

Its main functions include:

• Regulating blood pressure

• Maintaining blood sugar levels

• Supporting immune function in the short term

• Managing inflammation and stress responses

 Normal Daily Pattern:
Cortisol peaks in the early morning (around 8 AM) and gradually declines to reach its lowest levels around midnight.

When Is the Test Ordered?

Your doctor may request this test if you show signs of chronically elevated cortisol, such as:

• Unexplained weight gain (especially in the face or upper body)

• Rounded “moon face” appearance

• Muscle weakness or limb thinning

• High blood pressure or blood sugar without a clear cause

• Irregular menstrual cycles or low libido

• Early-onset osteoporosis

• Easy bruising or slow wound healing

Types of Late-Night Cortisol Tests

There are two common methods:

1. Salivary Cortisol Test

• Done at home using a collection device

• Sample collected between 11 PM and midnight

• Non-invasive, accurate, and easy to perform

• Widely used for screening Cushing’s Syndrome

2. Blood Cortisol Test

• Requires a blood draw in a clinic or hospital

• Performed late at night

• Less commonly used due to stress from blood draw possibly affecting cortisol levels

Normal Cortisol Levels at Night

• Salivary sample: Less than 100 ng/L (may vary by lab)

• Blood sample: Less than 5 µg/dL at midnight

⚠️ Always interpret results in the context of clinical symptoms and lab reference ranges.

What Does a High Cortisol Level at Night Mean?

A high level indicates dysregulation of the HPA axis (hypothalamic-pituitary-adrenal axis).

Possible causes include:

• Cushing’s Syndrome

• Pituitary tumors producing ACTH (Cushing’s Disease)

• Adrenal tumors

• Ectopic ACTH-producing tumors (e.g., in the lungs)

• Chronic stress or sleep disorders

• Use of corticosteroid medications

Is Low Nighttime Cortisol Dangerous?

This test is not typically used to diagnose cortisol deficiency, but very low levels may suggest:

• Adrenal insufficiency (Addison’s disease)

• Sudden withdrawal from long-term steroid therapy

• Pituitary gland disorders

 In such cases, further tests like morning cortisol or ACTH stimulation test are recommended.

How to Prepare for the Test

 Preparation tips:

• Avoid caffeine and smoking for 12 hours before the test

• Do not perform intense exercise on the same day

• Stay calm and relaxed before the test

• Discontinue corticosteroid medications if advised by your doctor

• For saliva collection, rest in a dark, quiet room before sampling

Frequently Asked Questions (FAQ)

❓ Can I perform this test at home?
Yes. Salivary cortisol tests are often done at home using sterile kits and sent to the lab.

❓ Is the late-night cortisol test enough to diagnose Cushing’s?
No. It is a screening tool and should be followed by confirmatory tests like:

• 24-hour urinary free cortisol

• Dexamethasone suppression test

• ACTH level test

❓ Do sleep disorders affect the results?
Yes. Irregular or disturbed sleep can lead to temporary elevation in nighttime cortisol.

❓ Can medications affect the results?
Absolutely. Drugs such as steroids, antidepressants, or birth control pills may alter cortisol levels.

Summary

The Late-Night Cortisol Test is a highly sensitive tool used to detect excess cortisol production, especially in suspected Cushing’s Syndrome or adrenal gland disorders. It helps assess the circadian rhythm of cortisol secretion and is often done using a simple saliva sample at home.

If your results are abnormal, don't panic—consult your doctor to run further confirmatory tests and reach a proper diagnosis.