Cortisol Test

A cortisol test, also known as the cortisol hormone test or serum cortisol test, measures cortisol levels in the blood during the early morning hours, when cortisol levels are naturally highest. Cortisol is often called the “stress hormone” because it primarily helps the body respond to physical and emotional stress. Cortisol is essential for regulating metabolism, maintaining blood pressure, controlling inflammation, supporting immune function, and helping the body maintain stable blood sugar levels.

The primary purpose of the cortisol blood test is to help doctors assess adrenal and pituitary gland function. The test may be used to investigate conditions associated with excessively low cortisol levels, such as adrenal insufficiency or Addison's disease, as well as disorders associated with excessive cortisol production, such as Cushing’s syndrome.

A doctor may recommend an 8 AM cortisol blood test if a person shows symptoms suggestive of abnormal cortisol production.

Symptoms of low cortisol levels include: 

• Persistent fatigue or unusual tiredness 
• Muscle weakness 
• Dizziness or fainting, especially while standing 
• Unexplained weight loss 
• Loss of appetite 
• Nausea, vomiting, or abdominal pain 
• Salt cravings 
• Low blood pressure 
• Darkening of the skin (hyperpigmentation) 
• Recurrent low blood sugar episodes 

Symptoms of high cortisol levels include:

• Rapid or unexplained weight gain, especially around the abdomen and face 
• Rounded “moon” face appearance 
• Excess facial hair growth in women 
• Fat accumulation between the shoulders (“buffalo hump”) 
• Purple stretch marks on the abdomen or thighs 
• Thin skin that bruises easily 
• Acne or oily skin 
• High blood sugar or diabetes 
• Mood changes, anxiety, depression, or irritability 
• Muscle weakness 
• Irregular menstrual cycles 
• Reduced libido

The cortisol test may also be recommended for individuals with: 

• Pituitary tumours
• Adrenal gland tumours
• Addison’s disease
• Cushing’s syndrome
• A history of pituitary surgery
• A history of adrenal surgery
• Long-term corticosteroid medicine use
• A history of radiation therapy involving the brain or adrenal glands

Cortisol testing is usually recommended in individuals with symptoms suggestive of abnormal cortisol levels, as follows:

A cortisol test helps doctors identify conditions linked to abnormal cortisol production and adrenal gland function. These include:

• Adrenal insufficiency: This condition occurs when the body does not produce enough cortisol. It may develop due to problems affecting the adrenal glands or pituitary gland.
• Addison’s disease: Addison’s disease happens when the adrenal glands cannot produce enough cortisol. Symptoms may include fatigue, dizziness, weight loss, and salt cravings.
• Cushing syndrome: Cushing syndrome develops when cortisol levels remain too high for a long period. People may experience weight gain, muscle weakness, facial puffiness, and high blood pressure.
• Pituitary gland disorders: The pituitary gland produces ACTH, a hormone that controls cortisol release. Pituitary disorders can interfere with normal cortisol production and hormone balance. 
• Stress-related hormonal dysfunction: Severe illness, surgery, infection, trauma, or physical stress may temporarily affect cortisol levels. Testing may help evaluate the body’s stress response during critical illness. 

What to Expect Before the Cortisol Test

No fasting is required for a standalone Cortisol test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Cortisol levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Cortisol Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes

The main parameter measured in a cortisol test is the cortisol level in the blood.

The normal cortisol range is shown in the table below.

Note: The normal range may vary slightly depending on the laboratory, testing method, and the individual’s health.

Note: Cortisol levels can also be temporarily affected by several non-disease factors, including:

• Emotional stress
• Pregnancy 
• Intense physical activity 
• Certain medications, such as steroid medicines or birth control pills. 

The cortisol blood test is generally considered safe. Most people experience no significant complications during sample collection. Some individuals may experience minor side effects, such as mild pain, slight bruising, or swelling; however, these typically resolve on their own.

Limitations of the Cortisol Test

The cortisol morning test has some limitations as:

• Cortisol levels naturally fluctuate throughout the day: They are typically highest in the early morning and lower at night. Incorrect sample collection timing may affect test results. 
• Stress can temporarily affect cortisol levels: Emotional stress, illness, surgery, infections, lack of sleep, or intense physical activity may temporarily increase cortisol levels.
• Certain medications can influence results: Steroid medicines, birth control pills, hormone therapy, and some anti-seizure medications may alter cortisol levels. Therefore, it is important to inform your physician about any ongoing medications.
• The cortisol test alone cannot diagnose a condition: Abnormal results usually require additional investigations to reach a diagnosis.
• Pregnancy may increase cortisol levels: Hormonal changes during pregnancy can naturally raise cortisol concentrations.

Since a single cortisol result may not always confirm the cause, doctors may recommend additional tests for further evaluation, which include:

• ACTH test
• ACTH stimulation test
• 24-hour urinary cortisol test
• Late-night salivary cortisol test
• Dexamethasone suppression test
• CT or MRI scan