Last evidence review: August 25, 2026
Medical note: This article is for education and does not diagnose Cushing syndrome. Cortisol testing is sensitive to timing, collection, sleep, medications, kidney function, pregnancy, illness, and assay method. A qualified clinician—usually an endocrinologist—should select and interpret testing when Cushing syndrome is suspected. Do not stop a prescribed steroid suddenly unless the prescriber gives you a tapering plan.
Cushing syndrome cannot be confirmed or excluded by one random cortisol result. The workup begins by checking for glucocorticoid exposure. If endogenous cortisol excess remains a concern, a clinician usually selects one suitable first-line test: two late-night salivary cortisol measurements, at least two 24-hour urinary free cortisol collections, or a clinician-directed 1-mg overnight dexamethasone suppression test. An abnormal result is commonly checked with another recommended measurement or method. The ACTH Test generally comes after endogenous hypercortisolism has been established; it helps classify the source as ACTH-dependent or ACTH-independent.
For broader testing guidance, see The Complete Guide to Lab Tests and Blood Work. For help understanding reference intervals, flags, thresholds, and trends, use How to Read and Understand Your Lab Results. To understand test selection, preparation, collection, and follow-up, review Direct-Access Lab Testing: How It Works and What to Expect.
Cushing syndrome describes the clinical effects of excessive glucocorticoid exposure over time. The exposure may come from medication or from cortisol produced inside the body. This distinction matters because the testing pathway is not the same for every cause.
Common symptoms—weight gain, fatigue, mood changes, poor sleep, acne, or high blood pressure—have many causes. Features that raise suspicion more strongly include easy bruising, facial redness, broad reddish-purple stretch marks, proximal muscle weakness, unexplained osteoporosis or fracture, and a pattern that becomes progressively more pronounced. In children, weight gain accompanied by slowing linear growth is especially important.
Because Cushing syndrome is uncommon and several first-line tests can be falsely abnormal, widespread testing of everyone with obesity, diabetes, depression, or fatigue can create more confusion than clarity. The Endocrine Society recommends testing people with multiple and progressive features, unusual findings for age, children who are gaining weight while falling in height percentile, and people with an adrenal incidentaloma compatible with an adenoma. A clinician may also test when the overall history or examination creates a high pretest probability.
Before biochemical testing, provide a complete medication and exposure history. Include:
If a steroid exposure is found, the next step is medication review with the prescriber—not unsupervised cortisol testing or sudden discontinuation.
Educational framework—not a diagnostic or treatment algorithm.
What not to use as the initial screen: a random serum cortisol, a routine morning cortisol, a random ACTH, or pituitary/adrenal imaging. These may be useful in other endocrine questions, but they do not reliably establish or exclude Cushing syndrome.
| Test and quick facts | What it shows and how it is used | Preparation, influences, and limitations |
|---|---|---|
| Late-Night Salivary Cortisol Use status: Common or first-line when clinically appropriate. Usually collected on at least two separate nights near the person’s usual bedtime. | Tests whether the normal late-night cortisol low point has been lost. Often convenient for home collection and useful when cyclic disease is suspected. | Sleep schedule, shift work, acute stress, smoking, eating, oral blood contamination, dental disease, collection timing, and assay method matter. The linked product measures one salivary cortisol specimen; Cushing evaluation generally requires at least two separately timed late-night measurements. Confirm the exact timing and repeat-order instructions before ordering. |
| Cortisol Free 24 Hour Urine Test with Creatinine Use status: Common or first-line when clinically appropriate. Usually at least two complete 24-hour collections. | Estimates unbound cortisol output across a full day. Particularly useful when cortisol excess is clear or more severe. | An incomplete or overcollected specimen can mislead. High fluid intake and collection-volume problems matter. Reduced kidney filtration may falsely lower urinary free cortisol, so it is less reliable in advanced chronic kidney disease. |
| 1-mg Overnight Dexamethasone Suppression Test Use status: Common or first-line; clinician-directed. A clinician prescribes dexamethasone at night and orders timed morning cortisol. | Tests whether dexamethasone appropriately suppresses the hypothalamic-pituitary-adrenal axis. Lack of suppression raises concern but is not a stand-alone diagnosis. | Oral estrogen can raise cortisol-binding globulin and total cortisol. Medicines that speed or slow dexamethasone metabolism can cause false results. Adherence and timing are critical. An optional Dexamethasone Test measures the drug concentration; it does not supply the prescription or replace the timed cortisol measurement. |
| ACTH Test Use status: Specialist-directed source classification. A time-sensitive blood specimen used after cortisol excess is confirmed. | Classifies endogenous hypercortisolism. Suppressed ACTH favors an adrenal source; nonsuppressed ACTH suggests pituitary or ectopic ACTH production. | ACTH is unstable and specimen handling matters. Timing, stress, and laboratory method can affect results. It is not a first-line screening test for Cushing syndrome. |
Healthy cortisol secretion follows a circadian rhythm: it is generally higher around waking and lower near habitual sleep. The Late-Night Salivary Cortisol approach asks whether that low point is preserved. Saliva reflects free cortisol and can be collected at home, avoiding the stress of a late-night blood draw.
Guidelines commonly call for two late-night measurements, not a single sample. Collection should match the person’s sleep-wake schedule. A conventional 11 p.m. sample may be inappropriate for a night-shift worker who sleeps during the day. Because reference limits and assay performance vary, interpret the reported laboratory range and method rather than importing a cutoff from another laboratory.
Do not eat, drink anything except water, smoke, brush or floss teeth, or use topical oral steroid products during the restricted period specified in the kit instructions. Blood from irritated gums can contaminate saliva. Follow the exact collection, refrigeration, and return instructions provided with the ordered product.
The Cortisol Free 24 Hour Urine Test with Creatinine measures cortisol not bound to carrier proteins as it is excreted over 24 hours. Creatinine and total volume help the clinician assess collection plausibility, but they cannot correct every collection error.
Collection usually starts after discarding the first morning urine. Every subsequent void is saved, including the first void at the same time the following morning. Missing one specimen can falsely lower the result; extending beyond 24 hours can falsely raise it. Follow the laboratory’s storage instructions. Because day-to-day production can vary, at least two collections are generally recommended.
Urinary free cortisol may be less informative in mild disease and can be falsely low when kidney function is substantially reduced. It is also less suited to proving a brief nighttime abnormality. On the other hand, markedly elevated and reproducible results can provide strong evidence of significant hypercortisolism when the collection is complete and confounders are addressed.
The 1-mg overnight dexamethasone suppression test asks whether a synthetic glucocorticoid can switch down ACTH signaling and morning cortisol production. In a common protocol, a clinician prescribes 1 mg of dexamethasone late in the evening and orders serum cortisol the next morning at a specified time. Protocols and interpretation must come from the ordering clinician.
A low post-dexamethasone cortisol indicates appropriate suppression. A result above a sensitive threshold such as 1.8 µg/dL indicates inadequate suppression and requires context; it does not, by itself, prove classic Cushing syndrome. Adherence, sampling time, oral estrogen, altered cortisol-binding globulin, and medicines that affect the CYP3A4 pathway can change the result. Examples include some antiseizure, antimicrobial, and other drugs. Do not stop or change medication without professional guidance.
The linked Dexamethasone Test measures the blood level of dexamethasone and may help explain an unexpected suppression result. The medication is not supplied by the laboratory; it requires a prescription and clinician-directed timing. A dexamethasone concentration without the corresponding timed cortisol does not constitute a suppression test.
Once endogenous hypercortisolism is convincingly established, the ACTH Test becomes useful. A low or suppressed result suggests that an adrenal source is making cortisol without ACTH stimulation. A measurable or elevated result suggests ACTH-dependent disease, most often pituitary Cushing disease or ectopic ACTH secretion.
ACTH is not an initial screening test because many people without Cushing syndrome can have results affected by time, stress, specimen handling, and normal biologic variation. It also cannot, by itself, separate pituitary from ectopic ACTH production. That distinction may require specialist testing and imaging.
| Situation | Why it matters | Typical testing implication |
|---|---|---|
| Shift work or irregular sleep | Clock time may not match the biologic late-night low point. | Saliva timing must match habitual sleep; another first-line method may be preferable. |
| Advanced kidney disease | Reduced filtration can lower urinary free cortisol excretion. | A clinician may prefer dexamethasone suppression over urinary free cortisol. |
| Pregnancy | Normal cortisol physiology and binding proteins change. | Testing requires pregnancy-specific expertise; the Endocrine Society favors urinary free cortisol and advises against dexamethasone suppression as the initial test. |
| Oral estrogen or high cortisol-binding globulin | Total serum cortisol may appear higher after dexamethasone. | Medication review and a different method may be needed. |
| Medicines that alter dexamethasone metabolism | Too little or too much dexamethasone exposure can produce a misleading result. | Choose another method or measure dexamethasone under clinician supervision. |
| Suspected cyclic Cushing syndrome | Cortisol may be normal between active phases. | Repeat late-night saliva or 24-hour urine during symptomatic periods; specialist follow-up is important. |
| Acute illness, pain, sleep loss, alcohol use, depression, or uncontrolled diabetes | Physiologic activation can create non-neoplastic hypercortisolism. | Stabilize reversible factors when possible and interpret repeated results with an endocrinologist. |
| Adrenal incidentaloma without overt Cushing features | The question is often MACS, not classic Cushing syndrome. | Use the adrenal-incidentaloma pathway, commonly including a clinician-directed 1-mg suppression protocol and confirmation of ACTH independence. |
Think of the workup as a series of questions, not a scorecard in which more ordered tests automatically create more certainty.
If clinical suspicion is low and a suitable, correctly collected test is normal, Cushing syndrome becomes less likely. When suspicion remains high—because features are progressive, an adrenal mass is present, or cyclic disease is possible—a normal result should not automatically end the evaluation. The clinician may repeat testing during a more symptomatic period or choose a different method.
Review the collection, medicines, sleep, kidney function, pregnancy status, illness, and laboratory method before labeling the result. A second recommended test helps determine whether the abnormality is reproducible. The 2026 Pituitary Society consensus notes that late-night salivary cortisol is commonly used to confirm mild or a single mildly abnormal result, while urinary free cortisol is commonly used when hypercortisolism is severe or clearly abnormal. That consensus focuses on biomarkers in ACTH-dependent disease, so it should not be treated as a complete guideline for every adrenal or medication-induced presentation.
Concordantly abnormal results from suitable tests—without a convincing non-neoplastic explanation—support moving to cause classification. This is where the ACTH Test belongs. Concordantly normal results generally make Cushing syndrome unlikely, except when cyclic disease or very high clinical suspicion remains.
Discordant results are not solved by averaging them. The clinician should ask whether the tests examined different parts of cortisol physiology, whether an error or confounder affected one specimen, and whether the condition is mild or cyclic. Endocrinology review is appropriate before adding imaging or a broad panel.
Small, clinically silent pituitary and adrenal lesions are common. Finding one before establishing cortisol excess can send the workup in the wrong direction. After ACTH classifies confirmed hypercortisolism, imaging can be targeted. In ACTH-dependent disease, pituitary MRI may be followed by additional biochemical tests or inferior petrosal sinus sampling when the source remains uncertain. In ACTH-independent disease, adrenal imaging is considered in the appropriate clinical setting.
Sustained cortisol excess can affect blood pressure, glucose regulation, potassium, cholesterol, kidney health, bone strength, infection risk, mood, and blood-clot risk. These measurements help assess health impact and treatment priorities, but they are not substitutes for cortisol case-detection tests.
Ferritin, vitamin B12, folate, thyroid, liver, and reproductive-hormone tests may be reasonable when a separate symptom or diagnosis supports them. They should not be presented as routine components of every Cushing syndrome workup.
Contact a healthcare professional promptly for rapidly worsening weakness, severe or difficult-to-control blood pressure, new diabetes symptoms, recurrent infection, marked mood or cognitive change, or a quickly progressive cluster of Cushing-compatible features. Seek emergency care for chest pain, severe shortness of breath, coughing blood, one-sided leg swelling, fainting, a new neurologic deficit, severe confusion, suicidal thoughts, or signs of a serious infection. These symptoms may signal a blood clot, cardiovascular event, psychiatric emergency, or infection and should not wait for routine direct-access testing.
Ulta Lab Tests provides direct access to selected laboratory tests where permitted. For suspected Cushing syndrome, access should support a defined clinical plan rather than encourage indiscriminate screening.
Before ordering: confirm the exact test name, specimen, collection timing, number of samples, preparation, medication instructions, and intended clinical question. Prices, availability, laboratory methods, and collection requirements can change.
For the broader commercial menu, visit the Cushing Syndrome testing category. A category or panel page can help locate available products, but it does not replace an endocrinologist’s diagnostic sequence.
Treatment depends on the cause and may include surgery, medication, radiation, or carefully managed changes in exogenous glucocorticoid therapy. Follow-up is individualized. Cortisol may be monitored with urinary, salivary, or serum measurements selected for the treatment used. Some patients need temporary glucocorticoid replacement after successful treatment because the normal hypothalamic-pituitary-adrenal axis has been suppressed.
Long-term follow-up also addresses blood pressure, diabetes, potassium, lipids, bone health, infection, mood, cognition, muscle function, and thromboembolic risk. Recurrence can occur, particularly after treatment for Cushing disease, so new or returning symptoms deserve reassessment rather than reliance on a single old result.
Use the Endocrine Disorders: Causes, Symptoms, Lab Tests, and Management pillar for a broad view of adrenal, pituitary, thyroid, pancreatic, and reproductive hormone disorders. For the opposite cortisol problem, see Adrenal Insufficiency and Cortisol Deficiency. The lifestyle-oriented guide How to Lower Cortisol Levels Naturally addresses everyday stress and sleep; lifestyle-related cortisol variation is not the same as endogenous Cushing syndrome.
Because cortisol excess can affect several body systems, related pillar guides include Diabetes and Prediabetes Blood Tests, Heart Health Blood Tests, Kidney Function Tests, and Healthy Aging and Longevity Blood Tests.
New to laboratory testing? Start with The Complete Guide to Lab Tests and Blood Work, learn context and reference intervals in How to Read and Understand Your Lab Results, and review access, preparation, and follow-up in Direct-Access Lab Testing: How It Works and What to Expect.
No. Morning cortisol varies widely and can overlap between people with and without Cushing syndrome. Recommended case-detection methods evaluate late-night loss of rhythm, 24-hour free cortisol output, or suppression after dexamethasone.
No. Stress, acute illness, pain, poor sleep, alcohol use, depression, uncontrolled diabetes, pregnancy, medicines, collection errors, and assay factors can raise or distort results. The pattern, clinical probability, and confirmation matter.
Usually not. A clinician selects the method most suitable for your sleep schedule, kidney function, pregnancy status, medications, suspected severity, and likelihood of cyclic disease. A different recommended test may then confirm an abnormal finding.
Cortisol changes from night to night, and one collection can be affected by stress, timing, food, smoking, oral blood, or collection error. Repeated measurements improve confidence that loss of the nighttime low point is reproducible.
Daily cortisol production and collection completeness vary. Repeating the measurement reduces the chance that one unusually high, low, incomplete, or overcollected specimen drives the conclusion.
It means cortisol did not suppress below a sensitive threshold in that protocol. It is not a stand-alone diagnosis. The clinician must review adherence, timing, medications, estrogen exposure, assay method, pretest probability, and whether the question is overt Cushing syndrome or MACS.
ACTH answers “where might confirmed cortisol excess be coming from?” It does not reliably answer “does this person have Cushing syndrome?” Using it too early can create misleading labels from normal variation or specimen-handling effects.
Not always. Testing during an inactive phase can be normal. If clinical suspicion remains high, an endocrinologist may arrange repeated late-night salivary or urinary free cortisol measurements during symptomatic periods.
Usually no. Incidental pituitary and adrenal findings are common. Biochemical confirmation and ACTH classification help determine which imaging, if any, is relevant.
No. Cushing syndrome includes every cause of chronic glucocorticoid excess. Cushing disease specifically means ACTH secretion from a pituitary tumor.
Yes. Steroid exposure is a common cause and may come from several routes. Never stop long-term or high-dose steroid treatment abruptly; the body’s own cortisol system may be suppressed.
No. A bundle may combine measurements that belong to different stages, have different collection requirements, or assess complications rather than diagnosis. Test selection and sequencing should be matched to a clinician’s plan.
The central principle is simple: timing and sequence turn cortisol measurements into a diagnostic evaluation. Late-night salivary cortisol, 24-hour urinary free cortisol, dexamethasone suppression, and ACTH are complementary only when each is used to answer the right question.
Update history: August 25, 2026 — Created as the canonical educational guide to the stepwise evaluation of suspected Cushing syndrome and reviewed against current endocrine guidance.
Disclosure: Ulta Lab Tests offers laboratory-testing services and may link to tests or panels discussed on this page. This content is educational and does not provide individual diagnosis or treatment.
These tests help assess metabolic, kidney, electrolyte, and cardiovascular effects. They do not diagnose Cushing syndrome.
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