Cortisol Blood Tests & Stress Markers Explained
Can a blood test measure stress? Not directly — but cortisol testing detects genuine adrenal disorders, and chronic stress leaves fingerprints across multiple blood markers. Here's what the science actually says.
The "Adrenal Fatigue" Myth: What Medicine Actually Says
"Adrenal fatigue" is a term popularised by alternative medicine practitioners to describe a collection of symptoms (fatigue, poor sleep, difficulty coping with stress, brain fog) allegedly caused by "exhausted" adrenal glands that can no longer produce adequate cortisol. This concept is not recognised by any endocrinology society in the world, including the Endocrine Society of Australia.
What the Evidence Shows
A 2016 systematic review in BMC Endocrine Disorders examined all available studies on "adrenal fatigue" and concluded there is no scientific basis for the concept. Patients diagnosed with adrenal fatigue show normal cortisol levels on validated tests. The symptoms attributed to adrenal fatigue are real, but they are caused by other conditions: depression, sleep disorders, anaemia, thyroid disease, vitamin deficiencies, or chronic fatigue syndrome.
Real Adrenal Conditions
Addison’s disease (primary adrenal insufficiency) and secondary adrenal insufficiency are genuine, serious conditions where the adrenal glands truly cannot produce enough cortisol. They require specific diagnostic tests (Synacthen stimulation test) and lifelong glucocorticoid replacement. Cushing’s syndrome is the opposite: excess cortisol production. Both are rare but important to diagnose correctly.
Types of Cortisol Tests
Serum Cortisol (Blood Test)
What it measures: Serum cortisol measures the total cortisol in your blood at a single point in time. Cortisol follows a strong diurnal rhythm: it peaks within 30–60 minutes of waking (the cortisol awakening response, or CAR), remains elevated in the morning, and gradually falls through the afternoon and evening, reaching its lowest point around midnight. A morning blood test (taken between 7–9am) is the standard first-line test because this is when cortisol should be at its highest. A very low morning cortisol suggests adrenal insufficiency, while a very high morning cortisol may suggest Cushing’s syndrome.
Normal ranges: Morning (7–9am): 170–540 nmol/L (varies by lab). Afternoon (4pm): 65–330 nmol/L. Late evening (11pm–midnight): below 170 nmol/L. Values outside these ranges may indicate adrenal pathology, but a single result is rarely diagnostic. Most endocrinologists require dynamic testing (stimulation or suppression tests) before making a diagnosis.
Clinical use: Screening for Cushing’s syndrome (cortisol excess) and Addison’s disease (cortisol deficiency). Morning cortisol below 100 nmol/L strongly suggests adrenal insufficiency. Morning cortisol above 500 nmol/L is usually normal and excludes adrenal insufficiency. Values between 100–500 nmol/L require a Synacthen stimulation test (synthetic ACTH injection) to clarify.
Limitations: Serum cortisol measures total cortisol (both protein-bound and free). Oral contraceptives and pregnancy increase cortisol-binding globulin, which raises total cortisol without changing free (active) cortisol — a common cause of apparently elevated cortisol in women. Stress, illness, pain, and even the anxiety of having blood drawn (white coat effect) can acutely elevate cortisol. A single high reading does NOT mean you have Cushing’s syndrome.
Salivary Cortisol
What it measures: Salivary cortisol measures free (unbound, biologically active) cortisol, which makes it unaffected by changes in binding proteins. Late-night salivary cortisol (collected at 11pm–midnight) is the preferred screening test for Cushing’s syndrome because cortisol should be at its lowest at this time — if it is elevated, it suggests loss of the normal diurnal rhythm, which is a hallmark of Cushing’s. Salivary cortisol can be collected at home, making it more convenient and less affected by the stress of a clinic visit.
Normal ranges: Late-night salivary cortisol: below 5.5 nmol/L (most Australian labs). Above this threshold on two separate occasions warrants further investigation for Cushing’s syndrome. Morning salivary cortisol: 5―25 nmol/L. The cortisol awakening response (CAR) is the sharp rise in cortisol in the first 30–45 minutes after waking — it is studied in research but not yet used in routine clinical practice.
Clinical use: Gold-standard screening for Cushing’s syndrome (two elevated late-night samples). Research applications include cortisol awakening response assessment and chronic stress profiling. Some functional medicine practitioners use 4-point salivary cortisol profiles (morning, noon, afternoon, night), but this is not part of mainstream Australian endocrinology and is not Medicare-funded.
Limitations: Contamination from food, drink, or blood (from bleeding gums) affects results. Patients must avoid eating, drinking, or brushing teeth for 30 minutes before collection. Smoking and alcohol on the day of testing can alter results. Shift workers have disrupted cortisol rhythms that make interpretation difficult. Salivary cortisol is NOT useful for diagnosing "adrenal fatigue" because this condition does not exist as a medical diagnosis.
24-Hour Urinary Free Cortisol
What it measures: This test measures the total amount of free cortisol excreted in urine over a full 24-hour period. By collecting urine for an entire day, it averages out the fluctuations caused by cortisol’s diurnal rhythm and provides a comprehensive picture of daily cortisol production. It is one of the three first-line screening tests for Cushing’s syndrome (along with late-night salivary cortisol and the overnight dexamethasone suppression test).
Normal ranges: 24-hour UFC: below 300 nmol/day (varies by lab and assay method). Values above 3–4 times the upper limit of normal are highly suggestive of Cushing’s syndrome. Mildly elevated values (1–3 times upper limit) require clinical correlation and repeat testing.
Clinical use: Confirmation of Cushing’s syndrome (elevated levels), monitoring treatment of Cushing’s syndrome, and distinguishing Cushing’s from pseudo-Cushing’s states (depression, alcohol excess, obesity) which can cause mild elevations.
Limitations: Incomplete urine collection (the most common source of error — even missing one void invalidates the test). Over-hydration falsely elevates results. Kidney impairment affects excretion. The test is inconvenient (carrying a collection jug for 24 hours) and has a high failure rate. It does NOT detect mild or cyclical Cushing’s syndrome reliably.
DHEA-S (Dehydroepiandrosterone Sulphate)
What it measures: DHEA-S is the most abundant steroid hormone in the body, produced primarily by the adrenal glands. It serves as a precursor to both testosterone and oestrogen. DHEA-S levels are stable throughout the day (unlike cortisol), making it easy to test at any time. It declines steadily with age, falling approximately 10–20% per decade after age 30. DHEA-S is sometimes ordered alongside cortisol when investigating adrenal function, as it provides independent information about the adrenal cortex.
Normal ranges: Age and sex-dependent. Males 18–39: 4.0–13.0 µmol/L. Males 40–59: 2.0–10.0 µmol/L. Males 60+: 1.0–6.0 µmol/L. Females 18–39: 2.5–11.0 µmol/L. Females 40–59: 1.5–8.0 µmol/L. Females 60+: 0.5–5.0 µmol/L.
Clinical use: Investigating adrenal tumours (very high DHEA-S suggests adrenal origin), evaluating androgen excess in women (PCOS, hirsutism, acne), and assessing adrenal function. Low DHEA-S may indicate adrenal insufficiency or chronic illness.
Limitations: The age-related decline in DHEA-S is normal physiology, NOT a disease. Despite marketing claims, DHEA supplementation has not been proven to reverse ageing, improve energy, or enhance cognition in well-designed clinical trials. The TGA (Therapeutic Goods Administration) classifies DHEA as a prescription-only medicine in Australia. DHEA-S is NOT a useful marker for "stress" or "burnout" in the absence of other clinical findings.
What Chronic Stress Actually Does to Your Blood Results
While you cannot measure "stress" with a single blood test, chronic psychological and physical stress leaves measurable effects across multiple markers. Your GP may recognise a pattern of stress-related changes even without ordering cortisol directly.
| Marker | Acute Stress | Chronic Stress | Mechanism |
|---|---|---|---|
| Blood glucose | Elevated (fight-or-flight response) | Elevated fasting glucose, insulin resistance | Cortisol increases hepatic gluconeogenesis and reduces insulin sensitivity |
| Total cholesterol & LDL | Mildly elevated | Persistently elevated LDL, reduced HDL | Cortisol stimulates hepatic cholesterol synthesis and lipogenesis |
| White blood cell count | Elevated (neutrophilia) | Mildly elevated with lymphopenia | Cortisol causes neutrophil demargination and lymphocyte redistribution |
| CRP / hs-CRP | Normal or mildly elevated | Persistently mildly elevated (1–3 mg/L) | Chronic stress promotes low-grade systemic inflammation |
| Thyroid (TSH) | Usually normal | TSH may be suppressed (euthyroid sick syndrome) | Cortisol suppresses TSH secretion and T4-to-T3 conversion |
| Testosterone | Variable | Reduced (especially in males) | Cortisol suppresses GnRH, reducing LH and testosterone production |
| Magnesium | Normal | May be depleted | Stress increases urinary magnesium excretion |
| Platelet count | Elevated | Normal or mildly elevated | Catecholamines mobilise platelets from the spleen |
When Cortisol Testing Is Genuinely Useful
Cortisol testing is medically indicated for specific clinical scenarios where adrenal pathology is suspected. It is NOT indicated for vague fatigue, general "stress," or burnout — these symptoms warrant other investigations first.
Suspected Cushing’s: moon face, central obesity, purple striae, easy bruising, proximal weakness
Suspected Addison’s: unexplained weight loss, hyperpigmentation, postural hypotension, salt craving
Adrenal incidentaloma found on imaging (CT/MRI)
Evaluation of pituitary tumour or pituitary insufficiency
Monitoring cortisol replacement in known adrenal insufficiency
Unexplained hypokalaemia or hyponatraemia (electrolyte disturbances)
Long-term corticosteroid use (assessing HPA axis suppression before tapering)
Recurrent hypoglycaemia without obvious cause
Feeling Stressed and Tired? Better Tests to Start With
If you are experiencing fatigue, brain fog, poor sleep, or difficulty coping — symptoms commonly attributed to "stress" or "adrenal fatigue" — your GP will typically order these investigations first, as they are far more likely to reveal a treatable cause:
Full blood count (anaemia, infection)
Thyroid function (TSH, free T4) — hypothyroidism mimics burnout
Iron studies (ferritin) — low iron causes fatigue even without anaemia
Vitamin D — deficiency causes fatigue and muscle weakness
Vitamin B12 — deficiency causes fatigue and cognitive changes
HbA1c / fasting glucose — diabetes and pre-diabetes cause fatigue
Liver function tests — hepatitis and liver disease cause fatigue
Kidney function (eGFR, creatinine) — chronic kidney disease causes fatigue
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Reference ranges sourced from the Royal College of Pathologists of Australasia (RCPA) and the Endocrine Society of Australia. SmarterBlood provides health information and AI-powered blood test analysis. It is not a substitute for professional medical advice, diagnosis, or treatment.