ACTH (Plasma) Biomarker Testing
An ACTH plasma test checks pituitary signaling to your adrenal glands and helps evaluate cortisol problems, with convenient ordering through Vitals Vault/Quest.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
ACTH (adrenocorticotropic hormone) is a signal your pituitary gland sends to your adrenal glands to tell them how much cortisol to make. Because ACTH and cortisol work as a feedback loop, measuring ACTH can help explain why your cortisol is low, high, or fluctuating.
This test is most useful when it is interpreted alongside a cortisol measurement taken at the same time of day. ACTH can change quickly with stress, sleep, and medications, so a single number rarely tells the whole story.
Your result can support clinician-directed evaluation of adrenal or pituitary conditions, but it cannot diagnose a specific disorder on its own.
Do I need a ACTH Plasma test?
You may want an ACTH plasma test if you are working through symptoms that could relate to cortisol imbalance, such as unusual fatigue, weakness, dizziness on standing, unexplained weight change, new stretch marks, easy bruising, muscle loss, or changes in blood pressure or blood sugar.
This test is also commonly ordered when a cortisol test is abnormal, or when your clinician is evaluating possible adrenal insufficiency, Cushing syndrome (cortisol excess), or a pituitary cause of hormone changes. It can be helpful if you have a history of long-term steroid use (pills, injections, inhalers, topical creams), because steroids can suppress your body’s ACTH and cortisol production.
You may not need ACTH as a first step if you are simply screening general health without symptoms. In that case, a morning cortisol (and sometimes DHEA-S) is often used first, and ACTH is added when the “why” behind cortisol results needs clarification.
If you are pregnant, acutely ill, or recently had surgery, ACTH and cortisol can shift in ways that are normal for those situations. Testing can still be appropriate, but timing and interpretation matter.
ACTH is measured in plasma using a CLIA-certified laboratory method; results should be interpreted with your symptoms, timing of collection, and companion hormone tests rather than used as a stand-alone diagnosis.
Lab testing
Order an ACTH (plasma) test through Vitals Vault and complete your draw through the Quest network.
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
With Vitals Vault, you can order an ACTH (plasma) test for a lab draw without needing to coordinate paperwork back and forth. Because ACTH is sensitive to collection timing and handling, it helps to use a consistent lab network and to follow the collection instructions you receive.
After your results post, PocketMD can help you make sense of how ACTH fits with your cortisol level, your collection time (often early morning), and common next-step questions to bring to your clinician. If you are trending symptoms over time, you can also use Vitals Vault to reorder and compare results across draws.
If your situation calls for a broader view, you can add companion testing (such as cortisol, electrolytes, or pituitary hormones) so your clinician has more context to interpret the pattern rather than a single isolated number.
- Order online and complete your draw through the Quest network
- PocketMD helps you prepare follow-up questions based on your results
- Easy retesting when your clinician wants confirmation or trend data
Key benefits of ACTH Plasma testing
- Helps explain whether an abnormal cortisol level is more likely adrenal-driven or pituitary-driven.
- Supports evaluation of adrenal insufficiency when symptoms and morning cortisol raise concern.
- Adds context in workups for cortisol excess (Cushing syndrome), especially when paired with cortisol testing.
- Helps assess suppression of the stress-hormone axis after long-term glucocorticoid (steroid) exposure.
- Guides what follow-up tests make sense next (repeat morning cortisol, stimulation testing, or pituitary evaluation).
- Improves interpretation when results are timed correctly, since ACTH follows a daily rhythm and stress response.
- Makes it easier to track changes over time when you repeat testing within the same lab network.
What is ACTH (plasma)?
ACTH (adrenocorticotropic hormone) is a hormone made by your pituitary gland, a small gland at the base of your brain. Its main job is to signal your adrenal glands (on top of your kidneys) to produce cortisol, which helps regulate energy, blood pressure, immune activity, and your body’s response to stress.
ACTH and cortisol operate as a feedback loop called the hypothalamic–pituitary–adrenal (HPA) axis. When cortisol is low, the brain increases ACTH to push the adrenals to make more cortisol. When cortisol is high, ACTH is usually suppressed to reduce cortisol production.
Because of that relationship, ACTH is rarely interpreted alone. A “high ACTH” can mean your body is trying hard to stimulate the adrenals, while a “low ACTH” can mean the pituitary is not signaling strongly or is being suppressed by medications or high cortisol.
ACTH also has a strong daily pattern. It is typically highest in the early morning and lower later in the day, and it can rise quickly with pain, anxiety, illness, low blood sugar, and sleep disruption.
What do my ACTH Plasma results mean?
Low ACTH levels
Low ACTH can happen when your pituitary is not signaling the adrenal glands strongly, or when ACTH is being suppressed by high cortisol or steroid medications. In practice, the meaning depends heavily on your cortisol result at the same time: low ACTH with high cortisol can fit patterns of cortisol excess, while low ACTH with low cortisol can suggest central (pituitary or hypothalamic) adrenal insufficiency or medication-related suppression. If you have been using glucocorticoids (including injections or high-dose inhaled steroids), suppression is a common reason for low ACTH. Your clinician may confirm with repeat morning testing and, when appropriate, dynamic testing such as an ACTH stimulation test.
In-range (expected) ACTH levels
An in-range ACTH result generally means your pituitary is sending a typical signal for the time of day the blood was drawn. Even with an in-range number, interpretation still depends on cortisol and symptoms, because you can have normal ACTH with abnormal cortisol in some conditions or during recovery from illness or steroid exposure. If you are monitoring treatment or recovery, your clinician may focus on whether ACTH and cortisol are moving in the expected direction over time rather than on a single draw. Always compare your result to the reference range used by your lab, since ranges and units can vary.
High ACTH levels
High ACTH often means your body is trying to stimulate the adrenal glands to produce more cortisol. When cortisol is low at the same time, a high ACTH pattern can be seen with primary adrenal insufficiency (when the adrenal glands cannot make enough cortisol). When cortisol is high, elevated ACTH can point toward ACTH-dependent cortisol excess, which can include pituitary-driven causes and other less common sources. Because stress and acute illness can raise ACTH, your clinician may repeat testing under stable conditions and add other tests to confirm the pattern.
Factors that influence ACTH
Timing matters because ACTH follows a circadian rhythm, so morning and afternoon results are not interchangeable. Physical or emotional stress, pain, low blood sugar, infection, and poor sleep can raise ACTH transiently. Medications are a major confounder: glucocorticoids (steroids) can suppress ACTH, while some drugs that affect dopamine or serotonin signaling can shift pituitary hormone output. Sample handling also matters for ACTH because it is less stable than many hormones, so following the lab’s collection instructions helps reduce misleading results.
What’s included
- Acth, Plasma
Frequently Asked Questions
Do I need to fast for an ACTH plasma test?
Fasting is not always required for ACTH, but many clinicians prefer a morning draw under consistent conditions, and fasting can help reduce stress-related variability from recent meals or low blood sugar swings. Follow the collection instructions you receive, and ask your clinician if they want ACTH paired with a morning cortisol at the same visit.
What time of day should ACTH be tested?
ACTH is usually highest in the early morning and lower later in the day, so many evaluations use an early-morning sample (often around 7–10 a.m.) and interpret it with a cortisol drawn at the same time. If your clinician is checking a specific pattern, they may request a different time, but you should not compare results from different times of day as if they were equivalent.
Should ACTH be tested with cortisol?
Yes, most of the clinical value comes from interpreting ACTH alongside cortisol. The combination helps your clinician decide whether a cortisol issue is more consistent with an adrenal problem (primary) or a pituitary/hypothalamic problem (central), and it can guide what confirmatory tests are appropriate.
Can stress or anxiety raise ACTH?
Yes. ACTH is part of your stress response, so acute anxiety, pain, illness, sleep loss, and even the stress of a blood draw can raise levels temporarily. If a result does not fit your symptoms or other labs, your clinician may repeat it under calmer, stable conditions.
Do steroids affect ACTH results?
They can affect ACTH significantly. Glucocorticoids (such as prednisone, dexamethasone, or high-dose inhaled or injected steroids) can suppress ACTH and cortisol production, sometimes for weeks depending on dose and duration. Tell your clinician about any steroid exposure so they can time testing appropriately and interpret results safely.
What does low ACTH with low cortisol mean?
That pattern can suggest central adrenal insufficiency (reduced pituitary or hypothalamic signaling) or suppression from steroid medications. It is not diagnostic by itself, so clinicians often confirm with repeat morning labs and may use dynamic testing (for example, an ACTH stimulation test) and additional pituitary hormone evaluation when indicated.
How soon should I retest ACTH if it’s abnormal?
Retesting depends on why it was ordered and how abnormal the pattern is. If the result may have been affected by timing, stress, or medication changes, your clinician may repeat a morning ACTH and cortisol within days to weeks under standardized conditions. If you are monitoring recovery after steroid use or treatment changes, retesting is often scheduled based on symptoms and a clinician-directed plan rather than a fixed interval.