The Cortisol Test measures the level of cortisol, a steroid hormone commonly known as the “stress hormone” because its production increases during physical or emotional stress.
Cortisol plays a crucial role in maintaining many essential body functions — it helps regulate metabolism, blood pressure, immune response, and the sleep–wake cycle, and it ensures the body can properly respond to stress.
Doctors recommend this test to evaluate adrenal gland function, stress-related disorders, or hormonal imbalances such as Cushing’s syndrome or Addison’s disease.
What Is Cortisol?
Cortisol is a glucocorticoid hormone, part of the steroid hormone family. It is vital for maintaining the body’s balance (homeostasis) and energy management.
When you experience stress — whether emotional (like anxiety) or physical (like illness or injury) — your brain signals the adrenal glands to release cortisol. This helps your body manage the situation by increasing glucose levels, controlling inflammation, and maintaining blood pressure.
However, both too much and too little cortisol can cause serious health problems. That’s why cortisol testing is an important diagnostic tool in endocrinology and general medicine.
Where It Is Produced in the Body
Cortisol is synthesized in the adrenal cortex, specifically in the zona fasciculata, which is the middle layer of the adrenal glands.
The adrenal glands sit on top of each kidney and are part of the endocrine system.
Cortisol production is regulated by a feedback loop involving:
- The hypothalamus (releases CRH — corticotropin-releasing hormone),
- The pituitary gland (releases ACTH — adrenocorticotropic hormone),
- The adrenal glands (produce cortisol in response to ACTH).
This is known as the HPA axis (Hypothalamic–Pituitary–Adrenal axis), which controls the stress response and maintains hormone balance.
Main Functions and Importance
Cortisol affects nearly every organ and tissue in the body. Its key roles include:
- Regulating metabolism: Helps in the breakdown of proteins, fats, and carbohydrates to maintain steady energy levels.
- Maintaining blood pressure: Supports normal cardiovascular function by influencing salt and water balance.
- Controlling inflammation: Acts as a natural anti-inflammatory hormone, preventing the immune system from overreacting.
- Regulating sleep–wake cycle: Cortisol levels are naturally highest in the morning (helping you wake up) and lowest at night.
- Helping the body respond to stress: Mobilizes energy stores, increases alertness, and prepares the body to handle challenges (“fight or flight” response).
Without balanced cortisol levels, your body’s metabolism, immune function, and stress regulation can be significantly disrupted.
Causes of Low Cortisol Levels
Low cortisol levels can indicate adrenal insufficiency or problems in the pituitary gland, which controls cortisol release. Common causes include:
- Addison’s disease: A condition where the adrenal glands cannot produce enough cortisol.
- Pituitary gland disorders: Low production of ACTH leads to reduced cortisol stimulation.
- Long-term use of corticosteroid medications: Suppresses adrenal function, leading to low cortisol.
- Infections or autoimmune conditions: May damage adrenal tissues.
- Sudden withdrawal from steroid therapy: Causes temporary adrenal suppression.
Symptoms of Low Cortisol Levels
When cortisol levels are too low, the body struggles to maintain energy, blood pressure, and metabolism. Symptoms may include:
- Chronic fatigue and weakness
- Low blood pressure and dizziness (especially when standing)
- Unintentional weight loss and poor appetite
- Darkening of the skin (especially in Addison’s disease)
- Nausea, vomiting, or abdominal pain
- Craving for salty foods due to low sodium balance
If untreated, severe adrenal insufficiency can lead to an adrenal crisis, a medical emergency characterized by very low blood pressure and shock.
Causes of High Cortisol Levels
High cortisol levels may be caused by chronic stress, hormonal imbalances, or certain diseases. Common causes include:
- Cushing’s syndrome: Overproduction of cortisol due to adrenal or pituitary tumors.
- Cushing’s disease: Specifically caused by a pituitary tumor that overproduces ACTH.
- Chronic stress: Continuous activation of the stress response raises cortisol over time.
- Adrenal tumors or hyperplasia: Lead to excessive hormone production.
- Prolonged corticosteroid medication use: Artificially increases cortisol levels.
Symptoms of High Cortisol Levels
Excess cortisol can affect many body systems. Typical symptoms include:
- Rapid weight gain, especially around the face (moon face), neck, and abdomen
- Purple stretch marks (striae) on the skin
- High blood pressure and diabetes
- Thin, fragile skin and easy bruising
- Slow wound healing
- Mood changes, such as anxiety, irritability, or depression
- Muscle weakness and osteoporosis (weak bones)
Long-term high cortisol can also suppress the immune system, increase infection risk, and cause hormonal imbalances.
Reference Ranges
Cortisol levels naturally vary throughout the day. They are highest in the morning and lowest at night. Typical reference ranges (may vary slightly by laboratory) are:
| Time of Day | Normal Range |
|---|---|
| Morning (8 a.m.) | 5–25 µg/dL (138–690 nmol/L) |
| Afternoon (4 p.m.) | 2–14 µg/dL (55–386 nmol/L) |
Doctors interpret cortisol results in context with symptoms, other hormone levels (like ACTH), and sometimes additional tests (such as a dexamethasone suppression test or ACTH stimulation test).
Sample Types and Testing Methods
The Cortisol Test can be performed using various sample types depending on the purpose:
- Blood (Serum):
- Most common method.
- Collected in the morning and/or evening to evaluate cortisol rhythm.
- Urine (24-hour collection):
- Measures total cortisol excreted in a day.
- Useful for diagnosing Cushing’s syndrome.
- Saliva (Late-night sample):
- Non-invasive test reflecting free cortisol levels.
- Helpful for detecting abnormal nighttime cortisol (seen in Cushing’s).
Test Preparation
- Timing matters: Cortisol levels change throughout the day, so follow your doctor’s timing instructions (usually morning or late-night).
- Medication disclosure: Inform your doctor about all medicines, especially steroids, oral contraceptives, or hormone therapy, as these affect results.
- Avoid stress and heavy exercise before testing to prevent temporary cortisol elevation.
- For urine collection: Follow the full 24-hour procedure carefully for accurate results.
When to Consult a Doctor
You should see a healthcare professional if you experience:
- Persistent fatigue, weakness, or dizziness
- Unexplained weight gain or loss
- Irregular blood pressure (too high or too low)
- Mood swings, anxiety, or sleep problems
- Physical signs of Cushing’s or Addison’s disease, such as stretch marks, dark skin patches, or swelling
The doctor may recommend hormone panels (like ACTH, DHEA-S, or 17-hydroxyprogesterone) to identify the cause of cortisol imbalance.
Important Word Explanations
- Cortisol: A steroid hormone that regulates metabolism, stress, and inflammation.
- Glucocorticoid: A class of steroid hormones that control glucose metabolism and immune function.
- Adrenal Glands: Small glands above the kidneys that produce cortisol and other hormones.
- ACTH (Adrenocorticotropic Hormone): A pituitary hormone that stimulates cortisol production.
- Cushing’s Syndrome: A condition of excessive cortisol production.
- Addison’s Disease: A condition of cortisol deficiency due to adrenal gland failure.
- HPA Axis: The hormonal control system linking the hypothalamus, pituitary, and adrenal glands.
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