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Synacthen Stimulation Test
345.00
The Synacthen Stimulation Test evaluates how well the adrenal glands produce cortisol. It is a key test for diagnosing adrenal insufficiency and related hormonal disorders.
Turnaround time
2 days
Biomarkers count
1
Same-Day Appointments
UKAS Accredited Labs
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Under 18? Patients under 18 can only be seen at GB Medlabs and Clinilabs, Monday to Friday only.
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Details about Synacthen Stimulation Test
What is the Synacthen Stimulation Test?
The Synacthen Stimulation Test, also known as the ACTH stimulation test, measures the adrenal glands’ ability to produce cortisol in response to synthetic adrenocorticotropic hormone (Synacthen). Cortisol is a vital hormone involved in stress response, blood pressure regulation, metabolism, and immune function.
During the test, baseline cortisol is measured, followed by administration of Synacthen, and repeat cortisol measurements are taken to assess adrenal responsiveness. A normal response indicates functioning adrenal glands, while an inadequate rise suggests adrenal insufficiency.
This test is widely used in endocrinology to evaluate both primary and secondary adrenal disorders.
Why do I need a Synacthen Stimulation Test?
Adrenal insufficiency can present with non-specific symptoms that are often overlooked or attributed to other conditions. Testing adrenal reserve is essential when cortisol production is suspected to be impaired.
You may need this test if you experience:
- Persistent fatigue or weakness
- Unexplained weight loss
- Low blood pressure or dizziness
- Salt cravings
- Nausea or abdominal pain
- Hypoglycaemia
- Poor stress tolerance
- History of long-term steroid use
- Abnormal cortisol blood results
The test helps clarify whether symptoms are due to adrenal dysfunction and supports further endocrine assessment.
Benefits of the test
- Gold-standard adrenal assessment
Widely accepted method for evaluating adrenal cortisol production. - Identifies adrenal insufficiency
Helps diagnose primary or secondary adrenal failure. - Clarifies borderline cortisol results
Useful when baseline cortisol levels are inconclusive. - Supports safe steroid management
Important for patients with current or previous steroid exposure. - Assesses stress hormone response
Evaluates the body’s ability to respond to physiological stress. - Guides endocrine investigations
Helps determine the need for further hormonal testing. - Objective and reproducible results
Provides measurable cortisol response data. - Improves diagnostic confidence
Reduces uncertainty in complex hormonal presentations.
Step-by-step: How we offer testing
Clinic-based testing (UK-wide)
- Choose your nearest UK clinic
- Attend your appointment
- Baseline blood sample taken
- Synacthen administered by a clinician
- Follow-up blood samples collected
- Samples sent to the laboratory for analysis
Home or hotel visit (+£60, UK-wide)
- Book a mobile clinician
- Blood samples taken at your home or hotel
- Synacthen administered safely on site
- No need to attend a clinic
- Samples securely transported to the laboratory
Your results explained
Low cortisol response (adrenal insufficiency)
- Cortisol fails to rise adequately after Synacthen
- UK standard: Peak cortisol typically <450–500 nmol/L
- Suggests impaired adrenal function
Normal cortisol response
- Cortisol rises appropriately after stimulation
- UK standard: Peak cortisol ≥450–500 nmol/L
- Indicates sufficient adrenal reserve
High or exaggerated response
- Cortisol rises well above expected thresholds
- UK standard: Significantly above 500 nmol/L
- Generally reflects normal or robust adrenal function
How It Works
Simple steps to get your results
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Book Online
Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
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Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
3
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
Take control of your health with London Blood Tests
WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.
Frequently Asked Questions
It evaluates the adrenal glands’ ability to produce cortisol.
No, it measures cortisol response after stimulation, not resting levels alone.
It is a key test used in the assessment of suspected Addison’s disease.
Long-term steroids can suppress adrenal function, which this test helps assess.
Not always; symptoms can be non-specific, making testing important.
Yes, it is commonly used in both.
Acute illness or stress can influence cortisol levels.
Yes, it helps assess secondary adrenal insufficiency.
It rules out significant adrenal insufficiency in most cases.
It suggests impaired adrenal cortisol production requiring endocrine evaluation.
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