ACTH Test: Purpose, Procedure, Normal Range, and Result Meaning

What is ACTH?

ACTH, also known as Adrenocorticotropic Hormone, is a hormone produced by the pituitary gland, a small gland located at the base of the brain.
Its main job is to stimulate the adrenal glands (which sit above the kidneys) to produce cortisol, the body’s primary stress hormone.

The ACTH test measures the amount of ACTH in the blood and helps evaluate the functioning of the pituitary gland, adrenal glands, and the hypothalamic-pituitary-adrenal (HPA) axis — the system that controls stress and metabolism.

Where is ACTH Produced in the Body?

ACTH is made and secreted by the anterior pituitary gland (adenohypophysis).
Its production is controlled by another part of the brain — the hypothalamus, which releases Corticotropin-Releasing Hormone (CRH).
CRH tells the pituitary to make ACTH, and ACTH in turn signals the adrenal glands to release cortisol.

This chain of control forms the HPA axis — a crucial communication system between the brain and adrenal glands.

Main Functions and Importance of ACTH

ACTH plays a vital role in maintaining hormonal balance and body function.
Its key functions include:

1. Stimulating Cortisol Production:
   The main job of ACTH is to stimulate the adrenal cortex (the outer part of the adrenal gland) to produce cortisol.
2. Regulating Metabolism:
   Cortisol helps the body use fats, proteins, and carbohydrates efficiently.
3. Managing Stress Response:
   Cortisol is often called the stress hormone — it helps the body respond to physical and emotional stress.
4. Supporting Immune Function and Blood Pressure:
   Adequate cortisol levels help control inflammation, maintain blood pressure, and support immune defense.
5. Maintaining Circadian Rhythm:
   ACTH and cortisol levels peak in the early morning and drop at night, following the body’s natural rhythm.

Causes of Low ACTH Levels

Low ACTH levels usually mean that the pituitary gland is not producing enough ACTH, or the adrenal glands are overproducing cortisol, which suppresses ACTH release.
Common causes include:

• Adrenal tumor or dysfunction (as in Cushing’s syndrome due to adrenal tumor)
• Long-term corticosteroid therapy (external steroid use suppresses ACTH)
• Pituitary damage or hypopituitarism
• High cortisol levels (negative feedback suppression of ACTH production)

Symptoms of Low ACTH Levels

• Fatigue and weakness
• Weight gain (especially around the face and abdomen)
• High blood pressure
• Mood changes or depression
• Increased body hair (in females)

Causes of High ACTH Levels

High ACTH levels usually mean that the pituitary or hypothalamus is sending too many signals to make cortisol, or that the adrenal glands are not responding properly.

Common causes include:

1. Addison’s Disease (Primary Adrenal Insufficiency)
   The adrenal glands fail to make enough cortisol, so ACTH increases to compensate.
2. Cushing’s Disease
   A pituitary tumor produces excess ACTH, causing overproduction of cortisol.
3. Ectopic ACTH Production
   Certain tumors (like small cell lung cancer) produce ACTH outside the pituitary.
4. Severe Stress or Illness
   Physical or emotional stress can temporarily increase ACTH.
5. Congenital Adrenal Hyperplasia (CAH)
   A genetic condition where enzyme defects cause hormone imbalance and high ACTH.

Symptoms of High ACTH Levels

• Darkening of skin (hyperpigmentation, especially in Addison’s disease)
• Fatigue and weight loss
• Low blood pressure and dizziness
• Nausea, vomiting, and salt cravings
• Moon face, central obesity, and purple stretch marks (in Cushing’s disease)

Reference Ranges

Normal ACTH levels can vary slightly between laboratories, but typical fasting morning values are:

🔸 Morning samples are preferred because ACTH naturally peaks early in the day.

Sample Type and Handling

How is the ACTH Test Performed?

1. A blood sample is drawn from a vein, usually from the arm.
2. The sample is collected in an EDTA tube and kept on ice to preserve the hormone.
3. The blood is then sent to the lab for plasma separation and ACTH measurement.
4. Sometimes, this test is done along with a Cortisol Test to evaluate both hormone levels together.

Interpreting ACTH Test Results

Test Preparation

• Blood sample should be taken in the morning (8–9 AM).
• Avoid stress before the test, as it can raise ACTH levels.
• Avoid steroid medications unless advised by your doctor.
• Fasting is not usually required, but your doctor may recommend it for accuracy.

When to Consult a Doctor

You should talk to a doctor if you experience:

• Chronic fatigue or muscle weakness
• Unexplained weight loss or gain
• Darkening of the skin (especially in folds or scars)
• Frequent dizziness or low blood pressure
• Changes in mood, depression, or anxiety

Your doctor may recommend ACTH and Cortisol testing together for a full hormone assessment.

Important Word Explanations

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