Acthp2mgdexplasmcnc
This blood test measures corticotropin (ACTH) levels in plasma after taking dexamethasone medication to help diagnose the cause of Cushing's syndrome.
{"Measures ACTH hormone levels after taking dexamethasone medication","Helps distinguish between pituitary and adrenal causes of excess cortisol","Involves taking a pill the night before blood draw","Blood sample is taken from a vein in your arm","Results help your doctor plan appropriate treatment"}
Key facts at a glance
- LOINC
- 50418-3
- Short code
- ACTH-DST
- Synonyms
- ACTH p 2 mg Dex Plas-mCnc
- Category
- chemistry
- Sample
- plasma
- Container
- Lavender top (EDTA) plasma tube - collect 1 mL plasma
- Units
- N/A
- Ref low
- 0
- Ref high
- 50
- Critical range
- — – 200 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Chemiluminescent Immunoassay (CLIA) or Electrochemiluminescence Immunoassay (ECLIA)
- CPT
- 82533
- SNOMED
- 313295004
- Specimen volume
- 1-2 mL of plasma
- Stability
- Plasma should be separated from cells within 1 hour. Store plasma at 2-8°C if testing within 24 hours; if delay >24 hours, freeze at -20°C or below. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The ACTH (corticotropin) test after dexamethasone suppression measures the level of adrenocorticotropic hormone in your blood after you take a dose of dexamethasone, a synthetic steroid medication. This test is part of the dexamethasone suppression test, which helps doctors determine the cause of abnormal cortisol levels and conditions like Cushing's syndrome.
Why do I need this test?
Your doctor may order this test if you have symptoms of excess cortisol (Cushing's syndrome), such as weight gain especially around the neck and face, high blood pressure, diabetes, easy bruising, or muscle weakness. The test helps distinguish between different causes: pituitary tumors (Cushing's disease), adrenal gland tumors, or ectopic ACTH-producing tumors.
How do I prepare for the test?
Your doctor will give you instructions to take 2 mg of dexamethasone by mouth the night before your blood test, typically around 11 PM. You may need to fast (not eat or drink anything except water) for a certain period before the test. Inform your doctor about all medications you are taking, as certain drugs can affect the results. Do not stop taking prescribed medications unless your doctor instructs you to do so.
What happens during the test?
A healthcare professional will draw a blood sample from a vein in your arm using a small needle. You may feel a brief stinging sensation. The blood will be collected in a tube and sent to a laboratory for analysis. The actual blood draw takes only a few minutes.
Are there any risks?
The risks associated with this test are minimal and include slight pain or bruising at the injection site, lightheadedness, or in rare cases, infection. Dexamethasone may cause temporary side effects such as insomnia, mood changes, or upset stomach. Contact your doctor if you experience any unusual symptoms.
When will I get my results?
Results are typically available within a few days to a week, depending on the laboratory. Your doctor will discuss the results with you and explain what they mean for your diagnosis and treatment plan.
Reference range
ACTH suppression to <50 pg/mL (post-dexamethasone) suggests pituitary source; lack of suppression may indicate ectopic ACTH production or adrenal Cushing'sN/A
Patient receives 2 mg dexamethasone orally at 11 PM the night before test. Blood sample is drawn at 8 AM the following morning. Patient should avoid glucocorticoids, estrogens, and drugs affecting ACTH secretion for at least 2 weeks prior. Inform laboratory of current medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Frequently asked questions
What is ACTH?
Why do I need to take dexamethasone for this test?
Can I eat or drink before the test?
What if I'm taking other medications?
Is this test safe during pregnancy?
Sources
- 1MedlinePlus - ACTH TestSource
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 15, 2026. · Read our editorial policy