What is Cortisol blood test? A complete guide

A cortisol blood test result shows your cortisol level at the time the sample was taken. A high or low result can have several explanations, including collection timing, illness and medicines. It cannot diagnose a stress problem or an adrenal condition on its own, so your GP will interpret it with your symptoms.

What is cortisol?

Cortisol is a hormone made by the adrenal glands, which sit above your kidneys. It helps regulate blood pressure and blood glucose, influences how your body uses energy, and affects inflammation.

Cortisol also helps your body respond to physical and emotional stress. Its normal daily pattern usually rises towards morning and falls in the evening. Shift work can change that pattern, so your sleep schedule is relevant when interpreting a result.

How to interpret your cortisol blood test result

Your cortisol result needs the reference interval for the laboratory, sample type and collection time. A morning blood result should not be compared with a late-night saliva result.

Check when the sample was taken and whether you followed any preparation instructions. Tell your GP about illness, disrupted sleep, night shifts and medicines, including hormonal contraception and corticosteroids. These details can change the meaning of a result.

The member comparison above describes results within a tested group. It is not a diagnostic threshold or a measure of how well you cope with stress. A result close to a member median does not exclude an adrenal disorder.

What can high cortisol mean?

A raised result may reflect temporary stress or illness, medicine effects or an endocrine condition. It needs further assessment if the pattern and symptoms suggest sustained cortisol excess.

Cushing's syndrome involves excessive cortisol exposure. Features can include easy bruising, muscle weakness and changes in body fat distribution. These symptoms overlap with other conditions, so an isolated raised blood result does not establish the diagnosis.

The RCPA describes cortisol testing in the context of adrenal assessment, often using stimulation or suppression tests. These tests assess how the body responds to a controlled signal, rather than relying only on a single resting measurement.

What can low cortisol mean?

A low result may need investigation for adrenal insufficiency, especially when it appears with symptoms such as unexplained weight loss, low blood pressure or persistent weakness. The collection time and medicines must still be considered.

Addison's disease is primary adrenal insufficiency, where the adrenal glands cannot make enough hormones. Problems involving the pituitary gland can also reduce cortisol production. Your GP may check ACTH, the hormone that signals the adrenal glands, or refer you for specialist testing.

An ACTH stimulation test measures whether cortisol rises appropriately after an ACTH-like medicine is given. NIDDK explains that this is commonly used to investigate adrenal insufficiency. Your clinician decides whether it is needed.

Blood and saliva cortisol results answer different questions

Blood and saliva samples are selected for a particular clinical question and are interpreted differently. A test that samples cortisol across a day is not automatically equivalent to the tests used to diagnose Cushing's syndrome.

For example, a clinician may use a specifically timed late-night saliva sample when investigating suspected cortisol excess. If further sampling is appropriate, the saliva cortisol test page explains Vively's available test and collection approach. Your GP should decide which diagnostic test fits your symptoms. Practitioners who use a saliva profile across the day, or the cortisol awakening response, can read our guide to salivary cortisol and CAR testing.

Cortisol tests do not diagnose “adrenal fatigue”. The Endocrine Society states that there is no scientific evidence for that diagnosis and no validated test for it. Persistent fatigue deserves assessment for recognised causes.

Practical steps after an abnormal cortisol result

Discuss the result with your GP before using a supplement or changing a medicine. A plan to lower everyday stress is different from treatment for an adrenal disorder.

• Bring the collection time, laboratory report and previous results to your appointment.
• List all medicines and supplements, including inhaled, topical, injected or oral corticosteroids.
• Describe symptoms and when they started, including changes in weight, strength, blood pressure or skin.
• Ask whether the result needs repeating under specific conditions or a different test is more appropriate.

A consistent sleep routine, manageable activity and support for ongoing stress can help wellbeing. They do not replace treatment for confirmed adrenal insufficiency or cortisol excess. Do not stop prescribed corticosteroids suddenly without medical advice.

For related context, read our explanations of DHEA-S results and hormone results in Australian adults.

When to seek medical care

Arrange GP review for an unexplained abnormal result or persistent symptoms. Seek emergency care for severe weakness with vomiting, severe abdominal pain, confusion or collapse, especially if you have known or suspected adrenal insufficiency. An adrenal crisis is a medical emergency.

How Vively can help

Vively is an Australian health membership. Our practitioners can help you understand blood results and discuss appropriate next steps alongside your GP. Our Baseline Health Check is a blood test covering 70+ markers; additional tests can be considered within a personal testing plan.

The blood and saliva test pages linked above cover current availability and collection details. You don't need a referral from your own GP. A doctor in our network still signs every request, and for tests other than the Baseline they sign it straight away, with no consult needed.

Frequently asked questions

Does a high cortisol result mean I am too stressed?

No. Stress can influence cortisol, but timing, illness and medicines can also affect a result. A single blood test cannot measure your stress burden or identify its cause. Discuss persistent stress symptoms with your GP even if your cortisol result falls within the laboratory reference interval.

Can a normal cortisol result rule out an adrenal condition?

Not always. The value depends on the collection time and the condition being investigated. If your symptoms suggest an adrenal or pituitary problem, your GP may arrange a specifically timed sample, a stimulation or suppression test, or specialist review. Do not dismiss ongoing symptoms based on one result.

Sources

1. Healthdirect: The role of cortisol in the body.
2. RCPA Manual: Cortisol.
3. NIDDK: Cushing's syndrome.
4. NIDDK: Diagnosis of adrenal insufficiency.
5. NIDDK: Adrenal insufficiency and adrenal crisis.
6. Endocrine Society: Adrenal fatigue.