These lab checks show if cortisol is low, high, or mistimed, and if the pituitary signal driving cortisol matches.
Cortisol and ACTH work as a pair. ACTH is made in the pituitary gland and tells the adrenal glands to release cortisol. Cortisol then feeds back to the brain so the body can dial the signal up or down. When symptoms or routine labs hint that this loop is off, clinicians often order cortisol testing, ACTH testing, or an ACTH stimulation test to see how the adrenals respond.
You will see a lot of numbers on a portal. The useful part is the pattern: sample type, time of day, and how ACTH and cortisol line up. This guide walks through what each test checks, how to prep, and what common result patterns usually lead to next.
What Cortisol And ACTH Do
Cortisol is a steroid hormone made by the adrenal glands. It affects blood sugar, blood pressure, and how your body uses fuel. Cortisol also follows a daily rhythm, often higher in the morning and lower late at night. A cortisol test can measure cortisol in blood, urine, or saliva, and each sample tells a slightly different story.
ACTH (adrenocorticotropic hormone) is a pituitary hormone that signals the adrenals to make cortisol. ACTH can change quickly, and it is also tied to the sleep-wake cycle. That is why the timing and handling of the blood sample matter for interpretation. MedlinePlus explains how ACTH testing is used with cortisol to help sort out adrenal and pituitary disorders.
Reasons Clinicians Order Cortisol And ACTH Testing
These tests are used to narrow down causes of symptoms that overlap with many conditions. Clinicians order them when adrenal insufficiency is a concern, when cortisol excess is suspected, or when a pituitary disorder is on the list. Testing can also be used to monitor known disorders or to check how treatment is working.
For suspected cortisol excess, doctors often start with screening tests and may use more than one type of test because a single check can miss cases. NIDDK notes that clinicians often use two screening tests to confirm Cushing’s syndrome. For suspected low cortisol, an ACTH stimulation test is commonly used to check whether the adrenals can raise cortisol after a signal.
Tests You May See And What Each One Adds
Cortisol Tests In Blood, Urine, Or Saliva
A cortisol blood test is often scheduled in the morning. Urine and saliva tests can help when the concern is cortisol excess, since they can capture output over time or during the late-night low point. MedlinePlus explains the main cortisol test types and why repeat testing may be used.
ACTH Blood Test
An ACTH blood test measures the pituitary signal in your bloodstream. Clinicians often pair ACTH with cortisol drawn at the same time. The pairing helps show whether the pituitary is sending a strong signal, a weak signal, or a signal that does not match the cortisol level.
ACTH Stimulation Test
The ACTH stimulation test measures how well the adrenal glands respond after you receive ACTH, often a synthetic form. Cortisol is measured before and after the dose. A normal rise can argue against adrenal insufficiency in many settings, while a blunted rise can point toward it. MedlinePlus describes this test as a way to measure adrenal response to ACTH.
How To Prep So The Numbers Mean More
Follow the lab instructions exactly. Timing is often part of the order, and a different draw time can change interpretation. If you are collecting urine or saliva, store samples the way the lab sheet says.
Share your medicine list with the ordering clinician. Steroid medicines can alter cortisol measurements and can lower ACTH through feedback. This includes pills, creams, inhalers, joint injections, and nasal sprays. Also mention estrogen therapy, since it can change cortisol binding in blood tests.
If you work nights or your sleep schedule is shifted, mention that before the test. Many reference ranges assume a morning draw tied to a typical sleep pattern. Your clinician can choose a testing plan that fits your real day.
| Test Or Step | What It Measures | How It Is Commonly Used |
|---|---|---|
| Morning serum cortisol | Cortisol at a set time | Initial screen in some settings; interpretation depends on draw time |
| Plasma ACTH | Pituitary signal to the adrenals | Paired with cortisol to help localize a problem to pituitary vs adrenal |
| ACTH stimulation test | Cortisol response after ACTH dose | Checks adrenal reserve when adrenal insufficiency is suspected |
| Late-night salivary cortisol | Cortisol near the usual nightly low point | Screening test for cortisol excess in some evaluation workups |
| 24-hour urinary free cortisol | Total cortisol output over 24 hours | Screening test for cortisol excess, often repeated for reliability |
| Dexamethasone suppression test | Whether cortisol suppresses after dexamethasone | Screening test used in some Cushing’s syndrome workups |
| Electrolytes and glucose | Salt, potassium, sugar patterns | Adds context when cortisol disorders are suspected |
| Renin and aldosterone | Salt and water regulation hormones | Often checked when primary adrenal insufficiency is suspected |
| Follow-up imaging | Pituitary or adrenal structure | Usually ordered after labs point toward a source |
Cortisol ACTH Test Timing And Handling Basics
ACTH and cortisol change across the day, so the lab order often specifies a draw time. If you arrive later than planned, tell the lab staff so your clinician can interpret the result in context. If you repeat testing, using the same lab can reduce method-to-method variation.
ACTH samples can be time-sensitive. Labs may chill the tube and process it quickly, since ACTH can break down. You do not need to manage this, yet it helps explain why clinics care about handling and timing.
For urine and saliva testing, collection accuracy matters. Missing part of a 24-hour urine collection can lower total output. Eating, drinking, or brushing teeth too close to a saliva sample can contaminate it, so follow the collection instructions closely.
How Clinicians Combine Cortisol And ACTH Results
Clinicians rarely rely on a single number. They review the ACTH and cortisol pair, the timing, and the test type. MedlinePlus notes that low ACTH with high cortisol can be seen in some cortisol excess patterns, while other pairings point in different directions.
If adrenal insufficiency is suspected, the Endocrine Society guideline for primary adrenal insufficiency describes ACTH measurement as part of diagnosis, with stimulation testing used to check adrenal response. If Cushing’s syndrome is suspected, NIDDK describes confirming the diagnosis with screening tests such as urine, saliva, or blood testing, then using follow-up tests to find the cause.
| Result Pattern | What It Can Point Toward | What Often Comes Next |
|---|---|---|
| Low cortisol with high ACTH | Primary adrenal insufficiency pattern | Stimulation testing, electrolytes, renin/aldosterone if ordered |
| Low cortisol with low or normal ACTH | Secondary adrenal insufficiency pattern | Stimulation testing, pituitary-focused evaluation if ordered |
| High cortisol with low ACTH | Adrenal source cortisol excess pattern or steroid exposure pattern | Medicine review, targeted adrenal testing if ordered |
| High cortisol with high ACTH | ACTH-driven cortisol excess pattern | Repeat screening tests, then source testing if ordered |
| Normal morning cortisol but symptoms persist | A rhythm issue can still be present | Late-night saliva or 24-hour urine testing if ordered |
| Normal stimulation response | Adrenal insufficiency less likely in many settings | Seek other causes; repeat only if the clinical picture changes |
| Blunted stimulation response | Adrenal insufficiency more likely | Determine primary vs secondary cause, then treatment planning |
Why A Result Can Look Odd Without A New Diagnosis
Timing Mismatch
A morning reference range is not meant for an afternoon draw. Late-night saliva needs a true late-night sample. If the timing was off, your clinician may repeat the test with tighter timing.
Medicine Effects
Steroid medicines can suppress ACTH and change cortisol readings. Stopping steroids suddenly can be unsafe, so do not change your medicine plan on your own. Instead, ask how your current medicines were handled in the testing plan.
Short-Term Illness Or Physical Strain
Acute illness and physical strain can raise cortisol. A single high number during a tough week may not match long-term cortisol excess. Clinicians often repeat screening tests when you are stable if symptoms still fit.
What To Expect During An ACTH Stimulation Test
The visit is structured and usually takes under a couple of hours. Blood is drawn, ACTH is given as an injection, then blood is drawn again at set times to measure cortisol response. MedlinePlus describes the test as measuring how well the adrenal glands respond to ACTH.
Bring your medicine list and the lab instructions. Ask whether you can eat and drink before the first draw. After the final sample, most people return to normal activity unless the clinic gives different directions.
Next Steps After You Receive Results
Portal ranges do not tell the full story. Your clinician will interpret results based on sample type, draw time, and your medicine history. If the result is borderline, a repeat test using a different method can sharpen the answer.
If results suggest adrenal insufficiency, clinicians may order more hormone tests and electrolyte checks, then build a treatment plan. If results suggest Cushing’s syndrome, NIDDK describes confirming with screening tests, then using follow-up testing to learn the cause. The process can take time because false positives happen and because steroid exposure can cloud results.
At your follow-up, ask three questions: Which exact test was used and at what time, what pattern the clinician sees across cortisol and ACTH, and what specific finding would change the plan. Those answers turn a long lab report into a clear next step.
When To Get Same-Day Medical Care
Seek same-day medical care for fainting, confusion, severe weakness, severe vomiting, or signs of dangerously low blood pressure. Those symptoms have many causes, and they are not the time to wait for a routine lab review.
If you have known adrenal insufficiency and you cannot keep down oral medicine due to vomiting, follow the emergency plan you were given and seek urgent care. If you do not have a plan yet, ask your clinician for one after your evaluation is complete.
References & Sources
- MedlinePlus.“Cortisol Test.”Explains blood, urine, and saliva cortisol testing and why repeat testing may be used.
- MedlinePlus.“Adrenocorticotropic Hormone (ACTH) Test.”Describes ACTH testing and how paired ACTH and cortisol results help narrow causes.
- Endocrine Society.“Primary Adrenal Insufficiency Guideline Resources.”Lists diagnostic testing elements for primary adrenal insufficiency, including ACTH measurement.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).“Cushing’s Syndrome.”Outlines screening tests used to diagnose Cushing’s syndrome and follow-up testing to find the cause.