By Dr. Matt Gianforte, D.C. | Functional Medicine Clinician
HPA axis testing measures cortisol, and sometimes ACTH, in blood, saliva, urine or hair to see how the hypothalamus, pituitary and adrenal glands are working together. The right test depends on the question: a 7 to 9 a.m. serum cortisol and an ACTH stimulation test for suspected adrenal insufficiency; late-night salivary cortisol, 24-hour urine or dexamethasone suppression for suspected cortisol excess; and a salivary curve for daily rhythm.
What does a cortisol result tell you if the sample was taken at the wrong time, measured with a different assay, or ordered for the wrong clinical question? That question sits at the center of HPA axis testing. Fatigue, sleep disruption, weight changes, anxiety, inflammation, and blood sugar swings can reflect many different conditions, so a broad “adrenal fatigue” label rarely provides a reliable diagnosis.
- HPA axis testing should answer a defined clinical question, such as adrenal insufficiency, cortisol excess, glucocorticoid-related suppression, or a disrupted daily rhythm.
- The hypothalamus, pituitary gland, and adrenal glands communicate through CRH, ACTH, and cortisol, with feedback signals that regulate output.
- A single morning cortisol can screen for adrenal insufficiency, but it doesn't fully evaluate dynamic reserve or cortisol excess.
- Salivary, urine, blood, stimulation, suppression, and hair tests measure different aspects of cortisol biology. They aren't interchangeable.
- Assay method, collection timing, medications, sleep schedule, and clinical symptoms can change interpretation.
- More testing isn't automatically better. The most useful result is the one that changes the next clinical decision.
What the HPA Axis Does and Why Testing Matters
HPA axis testing is most useful when it answers a specific question. It shouldn't be used to confirm a vague diagnosis of “adrenal fatigue,” because fatigue and poor stress tolerance can arise from endocrine disease, sleep disruption, medication effects, inflammation, nutritional problems, or many other causes.
The HPA axis, or hypothalamic-pituitary-adrenal axis, works as a communication circuit. The hypothalamus, a brain region involved in hormone regulation, releases corticotropin-releasing hormone, or CRH. CRH signals the pituitary gland to release adrenocorticotropic hormone, or ACTH, into the bloodstream. ACTH then tells the adrenal glands to produce cortisol.
Cortisol supports several essential processes, including blood pressure regulation, glucose availability, immune control, and adaptation to physical demands. Once cortisol rises, it sends negative feedback to the hypothalamus and pituitary. That feedback reduces CRH and ACTH, helping prevent excessive or prolonged activation.
Three different problems can affect the circuit
Primary adrenal insufficiency begins in the adrenal glands. The glands can't produce enough cortisol despite pituitary signaling, and aldosterone production may also be affected.
Secondary adrenal insufficiency begins higher in the circuit, often at the pituitary level. The adrenal glands may remain structurally intact but receive too little ACTH. Glucocorticoid exposure can suppress this signaling pathway, which makes medication history essential.
A third pattern involves functional HPA rhythm disruption, where the axis may respond differently under sleep loss, psychological stress, inflammation, illness, shift work, or inadequate recovery. This pattern mustn't be equated automatically with primary adrenal disease.
Clinical perspective: Symptoms can justify evaluation, but symptoms alone can't identify which part of the HPA axis is affected.
The value of testing lies in narrowing the differential diagnosis. A person with fatigue and dizziness may need evaluation for adrenal insufficiency, while someone with unexplained cortisol excess may need testing for Cushing syndrome. A person experiencing fatigue after glucocorticoid treatment may need a recovery-focused assessment rather than a broad cortisol panel.
Readers seeking broader guidance on laboratory evaluation can also review the guide to getting more out of your lab work. More information about the HPA axis and adrenal health is available through adrenal and HPA axis education.
Functional medicine practitioners usually start by asking what decision a cortisol result would change, then review sleep, symptoms and every medication, especially any oral, inhaled, topical or injected steroid, before choosing a test.
Comparing the Six Major HPA Axis Tests
Each cortisol test measures a different layer of physiology. Some assess baseline output, some map daily timing, and others challenge the axis or test its feedback loop.
| Test | Specimen & Timing | What It Measures | Primary Clinical Question | Key Strength | Main Limitation |
|---|---|---|---|---|---|
| Salivary diurnal cortisol | Saliva collected across the day | Free cortisol pattern and daily slope | Is the daily rhythm unusual? | Noninvasive and time-specific | Assay and collection quality vary |
| Cortisol awakening response | Saliva immediately on waking, then during the first hour | Rise after waking | Does cortisol increase appropriately after waking? | Captures an early dynamic response | Highly sensitive to waking-time accuracy and compliance |
| 24-hour urinary free cortisol | Urine collected across a complete 24-hour period | Integrated free cortisol excretion | Is cortisol production persistently excessive? | Useful in suspected cortisol excess | Incomplete collection can distort results |
| Morning serum cortisol | Blood, commonly between 7:00 and 9:00 a.m. | Total circulating cortisol at a defined time | Is adrenal insufficiency unlikely, likely, or uncertain? | Accessible screening test | A single value doesn't assess the entire axis |
| ACTH stimulation | Serum cortisol at baseline, then 30 and 60 minutes after synthetic ACTH | Adrenal reserve under stimulation | Can the adrenal glands respond to ACTH? | Directly challenges adrenal output | Cutoffs depend on assay method |
| Dexamethasone suppression | Cortisol after prescribed dexamethasone at a specified time | Feedback suppression | Does cortisol suppress appropriately? | Useful in cortisol-excess evaluation | Timing, medication interactions, and estrogen can affect interpretation |
The Cortisol Awakening Response commonly uses saliva immediately on waking, followed by samples at 30 and 60 minutes. Some protocols add daytime samples to describe the broader curve. Research indicates that cortisol generally rises after waking, reaches a peak about 30 minutes later, and declines toward its lowest nighttime level. A typical awakening response has been described as an increase of at least 2.5 nmol/L from baseline in compliant subjects (Shin et al., Yonsei Medical Journal, 2011).
Newer wearable and point-of-care cortisol technologies remain limited by calibration, matrix effects, reproducibility, and clinical standardization. They may eventually help with time-resolved monitoring, but a consumer-facing device shouldn't be treated as equivalent to a validated endocrine test.
People comparing hormone evaluations may find it useful to review how to balance hormones naturally, while women may benefit from this guide to hormone testing for women. A supplement isn't a substitute for selecting the correct test. For example, Cortisolv® 120 Capsules is a dietary supplement that combines Relora® (magnolia and phellodendron bark extracts), Sensoril® ashwagandha, Suntheanine® L-theanine and banaba leaf extract to support a healthy stress response, but supplementation should never delay evaluation for suspected adrenal disease.
Reading Cortisol Numbers With Clinical Context
Cortisol numbers only become meaningful when the reader knows when the sample was taken, what assay measured it, and which disease is being evaluated. A result that looks “low” at one time of day may be expected at another, and a threshold developed for one assay may not transfer safely to another.
For morning serum cortisol, clinical protocols commonly use a sample collected between 7:00 and 9:00 a.m. A value of 18 µg/dL or higher is commonly considered reassuring, a value below 3 µg/dL is considered insufficient, and results between 3 and 18 µg/dL are indeterminate (Sarkar et al., 2025, Table 1; Bowden, 2023). These bands guide the next step. They don't diagnose a patient in isolation.
The conventional ACTH stimulation test measures cortisol at baseline and after synthetic ACTH. Historically, a peak around 18 µg/dL, or approximately 497 to 500 nmol/L, has been used as a normal response (Bowden, 2023). Newer, more specific assays may support lower decision thresholds, roughly 14 to 15 µg/dL, because applying the older cutoff to these assays can label people as adrenally insufficient who are not (Bowden, 2023; Birtolo et al., 2023).
| Test | Typical Reference Range | Flag Range | Interpretive Note |
|---|---|---|---|
| Morning serum cortisol | 18 µg/dL or higher can be reassuring | Below 3 µg/dL can indicate insufficiency; 3 to 18 µg/dL is indeterminate | Interpret with ACTH, symptoms, medications, and assay |
| ACTH stimulation | Peak near 18 µg/dL has historically been used | Lower peaks may be concerning | Modern assays may use lower method-specific thresholds |
| Late-night salivary cortisol | Laboratory-specific | Elevated late-night results can support cortisol-excess screening | At least two measurements are recommended in guideline-based screening |
| Cortisol awakening response | Rise from waking baseline | A blunted or absent rise may be abnormal | The pattern matters more than one isolated value |
| 24-hour urinary free cortisol | Laboratory-specific | Increased excretion may support cortisol excess | Collection completeness and kidney function matter |
| Dexamethasone suppression | Expected suppression according to protocol and assay | Failure to suppress can be abnormal | Dose timing, estrogen, and interacting drugs affect results |
For suspected Cushing syndrome, late-night salivary cortisol has been reported with greater than 90% sensitivity and specificity (Raff, JCEM, 2009), and the Endocrine Society guideline recommends two late-night measurements when this test is used (Nieman et al., 2008). In a small study of 36 patients tested against insulin-induced hypoglycemia, a random salivary cortisol of 13.3 nmol/L had 89.3% specificity and 20.1 nmol/L had 87.5% sensitivity for abnormal HPA function with that study's assay (Karpman et al., Clinical Biochemistry, 2013).
Oral contraceptives and pregnancy can alter cortisol-binding proteins, while shift work changes the meaning of clock-based samples. A clinician interpreting cortisol imbalance should therefore review physiology and context before labeling a value abnormal.
Preparing for an HPA Axis Test the Right Way
Preparation begins with one question: What must the test determine? Preparation for adrenal insufficiency differs from preparation for Cushing syndrome or a daily rhythm assessment. Patients shouldn't change sleep, exercise, shift work, diet, or glucocorticoid use merely to produce a more favorable result.
Match collection habits to the test
For salivary diurnal testing, collection often occurs on a typical day at consistent windows, such as waking, shortly after waking, midday, evening, and bedtime. Patients should follow the kit instructions and generally avoid brushing teeth, eating, drinking, smoking, or exercising immediately before a saliva sample.
For the Cortisol Awakening Response, the first sample should be collected immediately upon waking, followed by samples at 30, 45, or 60 minutes according to the protocol. Record waking time, sleep quality, unusual stress, and any deviation from the schedule.
A 24-hour urine collection usually begins after the bladder is emptied. Every later void belongs in the container, which should be stored as directed, often refrigerated, and finished with a final collection at the end of the period.
Protect the interpretation
Serum cortisol and ACTH require precise timing. Supplements and medications should only be held if the interpreting clinician gives explicit instructions. Dexamethasone testing requires exact dose and timing, and vomiting, missed doses, estrogen exposure, or interacting medications can invalidate the result.
Hair cortisol may reflect longer-term exposure, but hair treatments, coloring, washing frequency, growth rate, and sampling location can affect the measurement.
Bring a complete medication and supplement list, recent steroid exposure, symptoms, sleep schedule, collection times, and any illness occurring around the test. Accurate context is part of the specimen.
Interpreting Results Through a Root-Cause Lens
A cortisol result should create a branching clinical decision, not a diagnosis of “adrenal fatigue.” The first branch asks whether the concern involves low cortisol, excess cortisol, medication-related suppression, or a disrupted rhythm without established primary adrenal disease.
Morning serum cortisol below the laboratory reference range becomes more concerning when it appears with low sodium, high potassium, low blood pressure, or high ACTH. That pattern may suggest primary adrenal insufficiency and requires medical evaluation. A low response during ACTH stimulation supports adrenal insufficiency when interpreted with baseline cortisol, ACTH, symptoms, and the assay used.
The opposite branch involves possible cortisol excess. High late-night salivary cortisol, increased 24-hour urinary free cortisol, or failure to suppress after dexamethasone can raise concern for Cushing syndrome. Those findings generally call for endocrinology evaluation rather than treatment with supplements alone.
| Test Pattern | Possible Meaning | Next Step |
|---|---|---|
| Low morning serum cortisol | Possible adrenal insufficiency or medication-related suppression | Review ACTH, medication history, electrolytes, and consider stimulation testing |
| Blunted ACTH-stimulated peak | Reduced adrenal reserve | Refer for endocrine evaluation and interpret with assay-specific limits |
| Elevated late-night salivary cortisol | Possible cortisol excess | Confirm according to endocrine protocol |
| Increased 24-hour urinary free cortisol | Possible sustained cortisol excess | Review collection quality and refer when persistent |
| Failure to suppress after dexamethasone | Possible impaired feedback suppression | Review medications and pursue endocrine evaluation |
| Flattened salivary curve or unusual CAR | Possible rhythm disruption, sleep effect, illness, or assay variation | Correct context, assess reversible drivers, and repeat selectively |
A low morning value or flattened curve can reflect sleep disruption, shift work, illness, psychological stress, medication effects, or collection error. Hair cortisol may describe longer-term exposure, but it can't identify a particular day or diagnose adrenal insufficiency.
A root-cause framework connects results with sleep loss, overtraining, caloric restriction, chronic infection, pain, trauma, alcohol excess, or exogenous steroids without claiming that the adrenal glands have “burned out.” This approach aligns with broader functional medicine principles, while preserving the need to identify established endocrine disease.
Limits of Cortisol Testing and When to Refer
More HPA axis testing doesn't automatically produce more useful information. Cortisol changes with time of day, sleep schedule, acute illness, pregnancy, exercise, alcohol, medications, and collection technique. Salivary assays can differ in analytical range, handling requirements, and reference intervals, so even a carefully collected result isn't a standalone diagnosis.
A single low cortisol value may reflect poor sleep or an unusual testing day. A normal value may not exclude intermittent cortisol excess. A borderline dexamethasone result may require confirmation rather than a functional label.
Hair cortisol introduces its own uncertainty. Hair growth, chemical treatment, washing, external contamination, and sampling location can alter interpretation. Urinary testing can also be affected by incomplete collection and kidney function.
Safety rule: A functional plan must never delay treatment or referral for suspected adrenal insufficiency or cortisol excess.
Prompt medical evaluation matters when suspected adrenal insufficiency occurs with vomiting, abdominal pain, hypotension, hypoglycemia, electrolyte abnormalities, or acute deterioration. Endocrinology referral also fits unexplained cortisol excess, abnormal dexamethasone suppression, markedly abnormal ACTH, a confirmed low ACTH-stimulated peak, or discordant results.
Before referral, document symptom onset, collection timing, oral, inhaled, topical, and injected glucocorticoids, other medications, supplements, and relevant laboratory values. A functional medicine plan may support sleep, nutrition, exercise recovery, and stress regulation, but it must not replace glucocorticoid treatment, urgent electrolyte management, or evaluation for pituitary and adrenal pathology.
Putting HPA Axis Testing Into a Functional Protocol
A practical protocol starts with the clinical picture, selects the narrowest validated test, and defines what result would change management.
| Clinical Picture | First-Line Test | Action Threshold | Next Protocol Step |
|---|---|---|---|
| Suspected adrenal insufficiency | Morning serum cortisol, followed by ACTH stimulation when indicated | Below 3 µg/dL is concerning; 3 to 18 µg/dL is indeterminate; a low assay-appropriate stimulated peak needs evaluation | Review ACTH, electrolytes, medications, and refer promptly when clinically concerning |
| Cortisol excess or possible Cushing syndrome | Late-night salivary cortisol, 24-hour urinary free cortisol, or dexamethasone suppression | Persistent elevation, increased urinary free cortisol, or failure to suppress | Confirm through an endocrine pathway |
| Glucocorticoid-related suppression | Morning serum cortisol during recovery planning | Use a continuum-based interpretation rather than one universal yes/no cutoff | Follow current clinician-directed taper and reassess when appropriate |
| Functional rhythm disruption without primary disease | Indication-specific salivary rhythm or CAR protocol | Persistent flattening or an unusual pattern with significant symptoms | Address sleep, nutrition, recovery, stress load, and competing diagnoses |
Four clinical pathways
Possible adrenal insufficiency requires medical triage first. A morning cortisol can screen, while ACTH and stimulation testing clarify whether the adrenal glands can respond. A confirmed low response, especially with concerning symptoms or electrolyte abnormalities, should trigger endocrine evaluation.
Possible cortisol excess needs a test designed to detect loss of the normal nighttime decline or impaired suppression. Functional interventions may support general health, but they shouldn't substitute for evaluation of Cushing syndrome.
Iatrogenic suppression requires a careful medication timeline. Current guidance places morning serum cortisol first during glucocorticoid recovery and doesn't recommend routine dynamic testing for every person tapering treatment (Endocrine Society glucocorticoid-induced adrenal insufficiency guideline).
Functional HPA dysregulation remains a diagnosis of context, not a single abnormal panel. The plan may prioritize regular sleep, adequate nutrition, gradual exercise recovery, and stress-regulation practices, followed by selective reassessment (see how to lower cortisol levels naturally). Some people also use adrenal-support formulas such as Adrenal Manager™, which combines adrenal glandular concentrates with rhodiola, L-tyrosine, vitamin C and B vitamins, but only after disease has been ruled out. A repeat interval of 8 to 12 weeks can be considered when a clinician needs to evaluate change over time, but testing should be tied to symptoms and an objective management question.
Any confirmed low ACTH-stimulated peak, 24-hour urinary free cortisol above the laboratory reference range, abnormal dexamethasone suppression, or persistent diurnal flattening with severe symptoms warrants escalation rather than endless self-testing. Readers exploring supplement context can review supplements for adrenal fatigue or browse hormone and adrenal support supplements, while remembering that supplements don't diagnose or replace endocrine care.
Medication note: don't stop or change prescribed medication, including any steroid, without talking to your clinician. Stopping glucocorticoids abruptly can be dangerous.
DrMattGianforte.com offers educational resources and clinician-curated supplements that can place HPA axis testing within a broader review of sleep, nutrition, metabolism, and stress physiology. Visit the drmattgianforte.com homepage to explore evidence-informed options, and work with your own clinician to decide which next step fits the clinical picture.
Frequently Asked Questions
What is the best HPA axis test for fatigue?
There isn't one universal best test for fatigue. A clinician may begin with morning serum cortisol when adrenal insufficiency is a concern, while suspected cortisol excess calls for late-night salivary cortisol, urinary free cortisol, or dexamethasone suppression. The correct choice depends on symptoms, medications, timing, and the condition under evaluation.
Can a single cortisol test diagnose adrenal fatigue?
No. “Adrenal fatigue” isn't an established diagnosis that a single cortisol result can confirm. Symptoms may be real, but interpretation should consider adrenal insufficiency, glucocorticoid suppression, sleep disruption, illness, and other causes of fatigue.
What time should morning cortisol be tested?
Morning serum cortisol is commonly collected between 7:00 and 9:00 a.m. (Sarkar et al., 2025). The interpreting clinician should account for shift work, sleep timing, medications, and the assay used.
How does an ACTH stimulation test work?
Synthetic ACTH challenges the adrenal glands, and serum cortisol is measured at baseline and again at 30 and 60 minutes (Bowden, 2023). A peak near 18 µg/dL has historically been used, but modern assays may require lower, method-specific thresholds.
Is salivary cortisol useful for Cushing syndrome?
Late-night salivary cortisol can be useful when screening for endogenous Cushing syndrome. Reported sensitivity and specificity exceed 90% in this setting, and the Endocrine Society guideline recommends two late-night measurements (Raff, 2009; Nieman et al., 2008).
Can sleep disruption change HPA axis results?
Yes. Sleep timing, shift work, acute illness, exercise, alcohol, medication use, and collection technique can all affect cortisol patterns. Patients should test under typical conditions and report unusual circumstances rather than trying to manipulate the result.
When should someone see an endocrinologist?
Endocrinology evaluation is appropriate for suspected adrenal insufficiency, persistent cortisol excess, abnormal dexamethasone suppression, markedly abnormal ACTH, or a confirmed low ACTH-stimulated cortisol response. Vomiting, abdominal pain, hypotension, hypoglycemia, electrolyte abnormalities, or acute deterioration require urgent medical attention.
References
- Bowden SA. “Current Screening Strategies for the Diagnosis of Adrenal Insufficiency in Children.” Pediatric Health, Medicine and Therapeutics, 2023. PubMed Central
- Cadegiani FA, Kater CE. “Adrenal Fatigue Does Not Exist: A Systematic Review.” BMC Endocrine Disorders, 2016. PubMed
- Endocrine Society. “Glucocorticoid-Induced Adrenal Insufficiency.” Clinical Practice Guideline
- Shin IY, Ahn RS, Chun SI, et al. “Cortisol Awakening Response and Nighttime Salivary Cortisol Levels in Healthy Working Korean Subjects.” Yonsei Medical Journal, 2011. PubMed Central
- Endotext. “Endocrine Testing Protocols: Hypothalamic Pituitary Adrenal Axis.” NCBI Bookshelf
- Raff H. “Utility of Salivary Cortisol Measurements in Cushing's Syndrome and Adrenal Insufficiency.” The Journal of Clinical Endocrinology & Metabolism, 2009. PubMed
- Nieman LK, Biller BMK, Findling JW, et al. “The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline.” The Journal of Clinical Endocrinology & Metabolism, 2008. PubMed Central
- Karpman MS, Neculau M, Dias VC, Kline GA. “Defining Adrenal Status with Salivary Cortisol by Gold-Standard Insulin Hypoglycemia.” Clinical Biochemistry, 2013. PubMed
- Erturk E, Jaffe CA, Barkan AL. “Evaluation of the Integrity of the Hypothalamic-Pituitary-Adrenal Axis by Insulin Hypoglycemia Test.” The Journal of Clinical Endocrinology & Metabolism, 1998. PubMed
- Birtolo MF, Antonini S, Saladino A, et al. “ACTH Stimulation Test for the Diagnosis of Secondary Adrenal Insufficiency: Light and Shadow.” Biomedicines, 2023. PubMed Central
- Sarkar S, Abeyagunawardena AS, Sinha R, et al. “Impact of Glucocorticoid Therapy on Hypothalamic-Pituitary-Adrenal Axis Function in Pediatric Nephrotic Syndrome: A Narrative Review.” World Journal of Clinical Pediatrics, 2025 (Table 1). PubMed Central
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