What is the ACTH (Adrenocorticotropic Hormone) Test?

The ACTH test measures the level of adrenocorticotropic hormone in the blood, a hormone produced by the pituitary gland that stimulates the adrenal glands to release cortisol. ACTH plays a central role in the body’s stress response, metabolism, immune regulation and blood pressure control.

ACTH and cortisol work together in a tightly regulated feedback loop known as the hypothalamic–pituitary–adrenal (HPA) axis. When cortisol levels are low, ACTH rises to stimulate production; when cortisol is high, ACTH is suppressed. Measuring ACTH provides insight into whether hormone imbalance originates from the pituitary gland or the adrenal glands.

This test is commonly used alongside cortisol testing to investigate suspected adrenal insufficiency, Cushing’s syndrome or pituitary dysfunction.

Why do I need a test for ACTH?

You may need this test if you have symptoms suggesting abnormal cortisol production or if previous blood tests show cortisol levels that are too high or too low. ACTH testing helps determine whether the underlying issue lies in the adrenal glands themselves or in the pituitary gland that controls them.

ACTH measurement is particularly important when symptoms are vague or overlap with common conditions such as fatigue, stress or weight changes. By clarifying the hormonal pathway involved, this test supports accurate diagnosis and targeted treatment.

Symptoms and scenarios where testing is recommended:

• Persistent fatigue or weakness
• Unexplained weight loss or weight gain
• Low blood pressure or dizziness
• Darkening of the skin (hyperpigmentation)
• Muscle weakness
• Mood changes or depression
• Suspected adrenal insufficiency (Addison’s disease)
• Suspected Cushing’s syndrome
• Abnormal cortisol test results
• Investigation of pituitary gland disorders

Benefits of the ACTH Test

• Differentiates adrenal from pituitary causes of cortisol imbalance
  Helps identify whether hormone dysfunction originates centrally or peripherally.
• Essential for diagnosing adrenal insufficiency
  Distinguishes primary adrenal failure from secondary (pituitary-related) causes.
• Supports investigation of Cushing’s syndrome
  Helps classify ACTH-dependent versus ACTH-independent cortisol excess.
• Clarifies unexplained cortisol abnormalities
  Adds essential context to cortisol test results.
• Guides further endocrine testing and imaging
  Results inform whether adrenal or pituitary imaging is required.
• Useful in monitoring known endocrine disorders
  Helps assess disease progression or response to treatment.
• Improves diagnostic accuracy in complex cases
  Particularly valuable when symptoms are non-specific.
• Simple but clinically powerful blood test
  Requires only a single blood sample with high diagnostic value.

Step-by-Step: How Testing Works

Choose your preferred testing method

You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.

Option 1 – In-Clinic Blood Draw

1. Select your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample, usually in the morning.
3. The sample is analysed for ACTH concentration.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a convenient time.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is packaged and transported to the laboratory promptly.
4. Results are uploaded digitally without the need to travel.

Access your report

You can download and share your results with your GP or endocrinologist for further interpretation.

Your Results Explained

Low Levels

Low ACTH levels suggest reduced pituitary stimulation of the adrenal glands.
This may indicate secondary adrenal insufficiency or suppression due to excess cortisol production.
Typical UK reference range: approximately 2–11 pmol/L (ranges vary by laboratory and time of day).

Normal Levels

Normal ACTH levels indicate appropriate pituitary signalling to the adrenal glands.
When combined with normal cortisol, this suggests a balanced HPA axis.

High Levels

Elevated ACTH levels indicate increased pituitary drive, often seen in primary adrenal insufficiency where the adrenal glands fail to produce cortisol.
High ACTH may also be seen in ACTH-dependent Cushing’s syndrome or ectopic ACTH production.
Results should always be interpreted alongside cortisol levels and clinical findings.