What is the Cortisol test?

The Cortisol test measures the concentration of cortisol in the blood. Cortisol is a steroid hormone produced by the adrenal glands and plays a vital role in regulating metabolism, blood pressure, immune response, and the body’s stress reaction.

Cortisol follows a diurnal rhythm, meaning levels are normally highest in the early morning and lowest at night. Because of this natural variation, the timing of the test is important and is usually performed in the morning unless otherwise specified.

This test is commonly used in endocrinology to investigate adrenal gland function and disorders related to cortisol imbalance.

Why do I need a Cortisol test?

Abnormal cortisol levels can affect multiple systems in the body and may contribute to fatigue, metabolic changes, mood disturbances, and blood pressure issues.

Testing cortisol helps identify whether symptoms are related to excess or insufficient cortisol production.

You may need a Cortisol test if you experience:

• Persistent fatigue or weakness
• Chronic stress or burnout symptoms
• Unexplained weight gain or weight loss
• Low or high blood pressure
• Sleep disturbances
• Anxiety, low mood, or irritability
• Muscle weakness
• Changes in blood sugar levels

Conditions commonly associated with abnormal cortisol levels include:

• Adrenal insufficiency
• Cushing’s syndrome
• Chronic stress-related disorders

Benefits of the Cortisol test

• Assesses adrenal gland function
  Evaluates cortisol production capacity.
• Supports investigation of chronic fatigue
  Helps identify hormonal causes.
• Identifies cortisol excess or deficiency
  Guides further endocrine testing.
• Supports diagnosis of adrenal disorders
  Used in standard endocrine practice.
• Provides insight into stress response
  Reflects physiological stress load.
• Simple and widely used blood test
  Requires only a single sample.
• Supports treatment planning
  Guides further investigation or referral.
• Clinically recognised hormone marker
  Used in NHS and private settings.

Step by step – how the test works

You can access Cortisol testing UK-wide through two options:

1. Clinic appointment
   Choose your nearest UK clinic. A healthcare professional will take your blood sample, usually in the morning.
2. At-home or hotel visit (£60 extra)
   A qualified phlebotomist visits your home or hotel, so you don’t need to travel.

Your sample is analysed in an accredited UK laboratory, and results are delivered securely.

Your results explained

Low cortisol levels

May indicate reduced adrenal function or adrenal insufficiency and can be associated with fatigue, low blood pressure, and weakness.

Typical UK reference range (morning):

• < 140 nmol/L

Normal cortisol levels

Suggest normal adrenal hormone production and stress response.

Typical UK reference range (morning):

• 140–690 nmol/L

High cortisol levels

May indicate excessive cortisol production, often associated with prolonged stress or endocrine disorders.

Typical UK reference range (morning):

• > 690 nmol/L

Reference ranges vary by laboratory and time of sample collection.