Understanding synacthen test results

Overview

The synacthen test (also called an ACTH stimulation test) checks how well your adrenal glands are working. These small glands on top of your kidneys make a hormone called cortisol, which helps your body handle stress, control blood pressure, and keep energy levels balanced. The test measures cortisol levels in your blood before and after a synthetic hormone is given. Low cortisol after the test can mean your adrenal glands are not making enough cortisol (a condition called adrenal insufficiency).

The synacthen test is a standard, common test used to evaluate adrenal function. The conditions it detects, such as adrenal insufficiency, are rare but serious.

The test is used for people who have symptoms that might suggest adrenal insufficiency. These include unexplained fatigue, weight loss, low blood pressure, darkening of the skin, or salt cravings. It can affect people of any age, including children and older adults.

Symptoms

Common symptoms

• Extreme tiredness that doesn't go away with rest
• Unintentional weight loss
• Low blood pressure (feeling dizzy or fainting when standing up)
• Darkening of the skin (especially on knuckles, scars, and inside the cheeks)
• Salt cravings
• Muscle weakness
• Nausea, vomiting, or diarrhea

Symptoms in children

• Slow growth or delayed puberty
• Frequent infections
• Excessive thirst and urination
• Irritability and poor feeding

Symptoms in older adults

• Confusion or memory problems that seem new
• Loss of appetite and weight loss
• Weakness and falls
• Symptoms mistaken for dementia or depression

Causes

Main causes

• Primary adrenal insufficiency (Addison's disease): The adrenal glands themselves are damaged, often by an autoimmune condition (the immune system attacks the glands). Other causes include infections (like tuberculosis) or rare genetic conditions.
• Secondary adrenal insufficiency: The pituitary gland in the brain doesn't produce enough ACTH, the hormone that tells the adrenals to make cortisol. This can be due to a pituitary tumor, head injury, or long-term use of steroid medications.
• Other causes: Some medications, certain infections, or bleeding into the adrenals (Waterhouse-Friderichsen syndrome) can also lead to adrenal insufficiency.

Risk factors

• Having an autoimmune condition (like type 1 diabetes, thyroiditis, or vitiligo)
• Long-term use of steroid medications (especially if stopped suddenly)
• Family history of autoimmune diseases
• Pituitary or adrenal tumors
• Infections such as tuberculosis or HIV
• Recent head trauma or pituitary surgery

When to see a doctor

See a doctor urgently if:

• If you have symptoms of an adrenal crisis (see emergency symptoms) – call your local emergency number immediately.
• If you have sudden severe vomiting, diarrhea, or inability to keep fluids down.
• If you feel extremely weak, confused, or unable to stand.

Book a routine appointment if:

• If you have ongoing tiredness, weight loss, or other symptoms that worry you.
• If you have a condition that may affect your adrenal glands (like an autoimmune disease).
• If you are taking steroid medications and have symptoms that suggest the dose may need adjusting.

Diagnosis

Doctors use the synacthen test along with other blood tests to diagnose adrenal insufficiency. The test is usually done in a hospital or clinic. You will have blood drawn to measure your baseline cortisol. Then you receive an injection of synthetic ACTH (synacthen). After 30 and 60 minutes, more blood samples are taken to see how your cortisol levels respond. If your cortisol does not rise normally, it suggests your adrenal glands are not making enough cortisol.

Tests that may be done

• Synacthen (ACTH stimulation) test
• Blood tests for cortisol and ACTH levels
• Blood tests for electrolytes (sodium and potassium)
• Adrenal autoantibodies to check for autoimmune causes
• Imaging tests (like CT scan of adrenal glands or MRI of pituitary) if needed

What to expect at your appointment

The test takes about 1 to 2 hours. You may feel a brief sting when the injection is given, and some people notice a metallic taste or mild nausea that goes away quickly. After the test, you can go home and resume normal activities. Your doctor will discuss the results with you, usually within a few days.

Treatment

If the synacthen test confirms adrenal insufficiency, treatment involves replacing the missing cortisol (and sometimes aldosterone) with medications. The goal is to mimic the body's natural hormone levels. There is no cure for primary adrenal insufficiency, but with proper treatment, most people lead full, active lives.

Self-care at home

• Always carry a medical alert card or bracelet stating you have adrenal insufficiency.
• Learn to adjust your medication dose during stress, illness, or injury (called 'sick day rules') – your doctor will teach you.
• Keep an emergency injection kit (with hydrocortisone) accessible at all times.
• Stay well hydrated and avoid skipping meals.

Medical treatments

Treatment involves taking hormone replacement medications daily. These include a corticosteroid to replace cortisol, and for some people, a mineralocorticoid to replace aldosterone (which helps balance salt and water). Your doctor will determine the right type and dose for you. The dose may need to be increased during times of stress, infection, or surgery. Regular follow-ups and blood tests help adjust the dose.

When is surgery considered?

People with adrenal insufficiency may need increased steroid doses before and after surgery or procedures. Always inform your surgeon and anesthetic team about your condition.

Living with this condition

Living with adrenal insufficiency requires daily medication and awareness. You will need to take your medications as prescribed, usually once or twice a day. You should also learn to recognize early signs of an adrenal crisis (like severe fatigue, dizziness, or nausea) and know when to seek help. Most people can work, travel, and enjoy hobbies with careful planning.

Lifestyle tips

• Establish a routine for taking medications at the same times each day.
• Wear a medical alert bracelet or carry an ID card.
• Keep a 'sick day' plan with your doctor for when you are ill.
• Consider joining a support group to connect with others.

Diet and exercise

Eat a balanced diet with regular meals. Some people may need extra salt, especially in hot weather or after sweating. Exercise is safe, but you may need to adjust your medication dose before intense activity – talk to your doctor. Stay hydrated and listen to your body.

Mental health and emotional wellbeing

Living with a chronic condition can be stressful. Anxiety, depression, or feeling overwhelmed are common. It's important to talk to your healthcare team about how you feel. Counseling or support groups can help. Remember, with treatment, you can live a full life.

Prevention

Most causes of adrenal insufficiency cannot be prevented. However, if you take long-term steroids, do not stop suddenly – work with your doctor to taper the dose. Also, get vaccinated against infections that might trigger a crisis (like flu or pneumonia).

Vaccines

Recommended vaccines include the annual flu shot and the pneumonia vaccine. Your doctor may also suggest other vaccines based on your health.

Screening programmes

Screening is not routine for the general public. However, if you have an autoimmune condition or a family history of adrenal insufficiency, your doctor may suggest testing if you have symptoms.

Complications

If left untreated

• Adrenal crisis – a life-threatening emergency with low blood pressure, shock, and loss of consciousness
• Severe weight loss and malnutrition
• Chronic fatigue and weakness that interferes with daily life
• Darkening of the skin (hyperpigmentation)
• Electrolyte imbalances (low sodium, high potassium) that affect heart and nerve function

Long-term outlook

With proper treatment, the outlook for people with adrenal insufficiency is excellent. Most people can live normal, active lives and have a near-normal life expectancy. The key is consistent medication, monitoring, and a good partnership with your healthcare team. Adrenal crises can be prevented with proper education and planning.

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