Can stress affect the four-specimen cortisol results?

Yes. Acute physical or psychological stress raises cortisol at any timepoint, particularly morning and midday. Patients should be rested, free from acute illness, and calm at each draw for valid interpretation.

Is fasting required before each blood draw?

No, fasting is not required. The key requirement is strict adherence to the scheduled draw times — morning, midday, afternoon, and late evening — aligned with the patient's habitual sleep-wake cycle.

How does shift work or jet lag affect this test?

Circadian misalignment from shift work or recent travel across time zones flattens or phase-shifts the diurnal rhythm, rendering results uninterpretable. Patients should maintain a stable sleep-wake schedule for at least three days before testing.

Do oestrogen or contraceptives interfere with cortisol measurement?

Yes. Oestrogen raises cortisol-binding globulin, which elevates total serum cortisol (the usual assay) while free cortisol remains normal. Women on oestrogen therapy may need salivary free cortisol or a correction factor for accurate interpretation.

Is this test diagnostic for Cushing syndrome or adrenal insufficiency?

No. The four-specimen profile is a screening and characterisation tool. Definitive diagnosis of Cushing syndrome requires confirmatory dynamic testing (dexamethasone suppression, 24-hour urinary free cortisol), and adrenal insufficiency requires an ACTH stimulation test.

How soon are results available?

Results are typically available within 2–3 business days from receipt of all four specimens at the Quest processing laboratory.

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Cortisol, 4 Specimens

Q: Why are four blood draws needed instead of one?

Cortisol varies several-fold across the day, peaking in the morning and reaching a nadir at night. A single value can be normal yet mask loss of the evening nadir or a flattened rhythm, both important for diagnosing Cushing syndrome and characterising HPA axis dysregulation.

Q: What does loss of the evening cortisol nadir indicate?

Persistently elevated late-evening cortisol (typically above 50–140 nmol/L depending on the assay) is one of the most specific screening findings for Cushing syndrome, indicating autonomous secretion that escapes normal circadian suppression.

The four-specimen cortisol test measures serum cortisol at morning, midday, afternoon, and late-evening timepoints to map the diurnal rhythm of the hypothalamic-pituitary-adrenal axis. It screens for Cushing syndrome by detecting loss of the evening nadir, characterises flattened rhythms in chronic stress and metabolic disorders, and supports investigation of adrenal insufficiency, interpreted…

Biomarkers

Blood (serum)

Sample

2–3 business days

Turnaround

Fasting

What is the Cortisol × 4 test?

The four-specimen cortisol profile maps the diurnal rhythm of the hypothalamic-pituitary-adrenal axis by sampling at morning, midday, afternoon, and late-evening timepoints. It is ordered when a single random cortisol is insufficient — when the clinician needs to distinguish physiological variation from pathological hypercortisolaemia, to screen for Cushing syndrome with greater specificity than isolated morning sampling, to detect loss of the evening nadir, or to characterise the flattened diurnal rhythm seen in chronic stress, metabolic dysregulation, and certain psychiatric conditions. Because cortisol secretion is pulsatile and varies several-fold across the day, a single value can fall within reference limits yet mask important rhythm abnormalities. The four-specimen approach captures the shape of the curve rather than a snapshot, and the late-evening sample in particular adds diagnostic power: loss of the physiological nadir is one of the most reliable screening signs of autonomous cortisol secretion. Practitioners use this profile to refine the pre-test probability before committing to more invasive dynamic testing.

What does the Cortisol × 4 test measure?

Cortisol AM(Morning Cortisol (08:00))

Range: Morning (08:00): approximately 140–690 nmol/L (5–25 µg/dL); diurnal reference intervals are assay- and time-specific.Optimal: A robust morning cortisol (>400 nmol/L or >14.5 µg/dL) generally excludes primary adrenal insufficiency in unstressed individuals, though dynamic stimulation testing remains definitive.nmol/L / µg/dL

Cortisol, the principal glucocorticoid synthesised in the zona fasciculata of the adrenal cortex, follows a circadian rhythm driven by hypothalamic-pituitary-adrenal axis pulsatility. Secretion peaks in the early morning (30–45 minutes after waking, the cortisol awakening response), maintaining glucose homeostasis, cardiovascular tone, and immune modulation during the fasting state. Morning cortisol represents the zenith of physiological output and is the most sensitive single timepoint for detecting primary adrenal insufficiency.

Morning cortisol is the cornerstone for screening suspected adrenal insufficiency; a value below 100 nmol/L (approximately 3.6 µg/dL) suggests impaired reserve and warrants dynamic testing. It is also elevated in Cushing syndrome, though overlap with physiological stress and obesity limits specificity without serial or suppression testing.

Cortisol Midday(Midday Cortisol (12:00))

Range: Midday (12:00): approximately 80–350 nmol/L (3–13 µg/dL); values decline through the day.Optimal: Midday cortisol should fall noticeably below the morning value; persistence near morning levels warrants investigation of circadian disruption or hypercortisolaemia.nmol/L / µg/dL

By midday cortisol secretion has begun its physiological decline from the morning peak. The slope of this decline reflects the integrity of central circadian regulation and negative feedback; a flat or inverted diurnal rhythm can signal chronic stress exposure, disrupted sleep-wake cycles, or autonomous hypersecretion.

Midday cortisol helps establish the diurnal profile. A value inappropriately close to the morning level suggests a flattened rhythm, seen in chronic stress states, sleep disorders, and some cases of subclinical or cyclical Cushing syndrome.

Cortisol PM(Afternoon Cortisol (16:00))

Range: Afternoon (16:00): approximately 50–250 nmol/L (2–9 µg/dL); continuing decline toward evening nadir.Optimal: Afternoon cortisol should continue to decline from midday, demonstrating preserved negative feedback and circadian control.nmol/L / µg/dL

The afternoon sampling point captures the descending limb of the diurnal curve, reflecting progressive negative feedback and diminishing ACTH drive. A normal downward trend supports intact hypothalamic-pituitary regulation.

Afternoon cortisol extends the diurnal map. An inappropriately elevated or flat afternoon value further characterises rhythm abnormalities and adds specificity to suspected Cushing syndrome when combined with late-evening sampling.

Cortisol Late(Late-Evening Cortisol (23:00))

Range: Late evening (23:00): typically <50 nmol/L (<1.8 µg/dL); the nadir of the circadian rhythm.Optimal: Late-evening cortisol should reach a clear nadir, typically below 50 nmol/L; higher values suggest loss of circadian rhythm or cortisol excess.nmol/L / µg/dL

Late-evening cortisol marks the circadian nadir, coinciding with the onset of melatonin secretion and peak sleep propensity. At this point cortisol output is maximally suppressed, and even mild elevations lose the overlap with physiological stress seen during daytime sampling.

Loss of the evening nadir — late-night cortisol persistently above 140 nmol/L (5 µg/dL) or, depending on the assay, >50 nmol/L — is one of the most specific screening findings for Cushing syndrome. It detects autonomous secretion that escapes normal circadian suppression.

Slope(Diurnal Cortisol Slope)

Range: Normal: steep decline from morning to late evening; abnormal: flat, blunted, or inverted rhythm.Optimal: A well-preserved diurnal rhythm shows a clear peak-to-trough difference, typically threefold or greater between morning and late evening.Qualitative pattern

The diurnal slope integrates the four timepoints into a pattern that reflects hypothalamic-pituitary-adrenal axis integrity, circadian gene expression, and the feedback sensitivity of the axis. A steep slope confirms robust regulation; a flat slope points to chronic stress, sleep disruption, or neuroendocrine dysregulation.

Assessing the overall slope adds interpretive power beyond single values. A flattened diurnal rhythm has been associated with chronic stress, metabolic syndrome, mood disorders, and certain cancers, while an exaggerated or chaotic rhythm may appear in severe stress or cyclical Cushing syndrome.

Why is the Cortisol × 4 test ordered?

Investigation of suspected Cushing syndrome when clinical features (central adiposity, proximal myopathy, striae, hypertension, glucose intolerance) warrant biochemical screening beyond a single cortisol or when salivary cortisol is unavailable
Evaluation of a flattened or disrupted diurnal rhythm in patients with treatment-resistant hypertension, early osteoporosis, or unexplained metabolic syndrome
Assessment of chronic stress states, burnout, or adrenal dysregulation in functional-medicine contexts, interpreted cautiously as a physiological rather than diagnostic finding
Characterisation of diurnal cortisol dynamics in patients with mood disorders, chronic fatigue, or fibromyalgia, where neuroendocrine dysregulation is suspected
Pre-operative endocrine work-up in patients with adrenal incidentalomas, to rule out subclinical or cyclical hypercortisolaemia before proceeding with imaging surveillance or surgery
Serial monitoring of diurnal rhythm restoration during treatment of hypercortisolaemia or as part of integrative stress-reduction interventions, though this is not a validated diagnostic endpoint

Sample collection and turnaround

Sample type

Blood (serum)

Fasting required

Collection method

Venipuncture at patient service centre

Turnaround

2–3 business days

Collection notes

Phlebotomy at a Quest draw site. Four timed blood draws are required: morning (ideally 08:00, within one hour of habitual waking), midday (12:00), afternoon (16:00), and late evening (23:00). Strict adherence to clock times is essential; patients must maintain their usual sleep-wake schedule for at least three days before testing, and shift workers or those with recent jet lag should defer the test. The patient should be rested and calm at each draw to minimise stress artefact, particularly for the late-evening specimen, which may require a home phlebotomy service or an evening draw site if logistically feasible. Document any acute illness, stressors, or medications (particularly oestrogen or exogenous glucocorticoids) at the time of each draw.

Specimen requirements

Minimum 0.5 mL serum per timepoint (four separate tubes, each labelled with collection time). Separate from cells within two hours and refrigerate or freeze if shipping is delayed. Specify the performing laboratory assay (immunoassay vs LC-MS/MS) for interpretation of reference intervals and cross-reactivity considerations.

What can affect Cortisol × 4 results?

elevatesAcute physical or psychological stress

Any stressor — illness, pain, anxiety, or even venepuncture itself — activates the HPA axis and can raise cortisol at any timepoint, particularly morning and midday, making stress state a critical element of clinical interpretation.

variableShift work, jet lag, and sleep deprivation

Circadian misalignment flattens or phase-shifts the diurnal rhythm; results are valid only when sampling times align with the patient's habitual sleep-wake schedule.

elevatesOestrogen and hormonal contraceptives

Oestrogen raises cortisol-binding globulin, elevating total cortisol (the usual assay target) while free cortisol may remain normal; salivary free cortisol or a correction for CBG is preferable in women on oestrogen therapy.

elevatesObesity and metabolic syndrome

Obesity increases cortisol production and clearance, often with modestly elevated 24-hour secretion but preserved diurnal rhythm and normal dynamic suppression, complicating the distinction from true Cushing syndrome.

elevatesAlcohol and chronic liver disease

Alcohol acutely stimulates the HPA axis, and cirrhosis impairs cortisol clearance and can raise CBG; both may produce 'pseudo-Cushing' biochemistry that resolves with abstinence or treatment of liver disease.

variableAssay method and specimen handling

Immunoassays measure total cortisol and can cross-react with synthetic steroids; LC-MS/MS is more specific. Delayed separation or haemolysis may alter results, and reference intervals are method-dependent.

What do Cortisol × 4 results mean?

Elevated

Hypercortisolaemia with loss of diurnal rhythm: Cushing syndrome (pituitary, adrenal, or ectopic ACTH), subclinical or cyclical hypercortisolaemia, pseudo-Cushing states (obesity, alcohol, depression, poorly controlled diabetes). An elevated late-evening cortisol (>50–140 nmol/L depending on assay) with a flattened curve is the most specific pattern for true Cushing syndrome and warrants confirmatory dynamic testing (low-dose dexamethasone suppression, 24-hour urinary free cortisol, late-night salivary cortisol).

Normal

A robust morning peak (>400 nmol/L), progressive decline through the day, and a clear late-evening nadir (<50 nmol/L) with a threefold or greater peak-to-trough ratio indicate intact HPA axis regulation and make Cushing syndrome and significant adrenal insufficiency unlikely. Normal diurnal rhythm also supports good circadian and metabolic health.

Reduced

Low morning cortisol (<100–140 nmol/L) with a blunted diurnal range raises suspicion for primary or secondary adrenal insufficiency, though a four-specimen profile is not the standard diagnostic test — an ACTH stimulation test is definitive. Chronic exogenous glucocorticoid suppression, hypopituitarism, or adrenal destruction (autoimmune, infectious, haemorrhagic) are the principal causes.

Note: Cortisol results are exquisitely sensitive to the timing and circumstances of collection. Sampling must follow a strict clock-time schedule aligned with the patient's habitual sleep-wake cycle; shift workers and recent trans-meridian travellers cannot be reliably assessed. Acute stress, illness, oestrogen therapy, and obesity all confound interpretation. Total serum cortisol measures both bound and free hormone; women on oestrogen and patients with altered binding-protein concentrations (pregnancy, cirrhosis, nephrotic syndrome) may need salivary free cortisol or direct free-cortisol assays. The four-specimen profile is a screening and characterisation tool, not a stand-alone diagnostic test — dynamic testing (suppression or stimulation) is required to confirm Cushing syndrome or adrenal insufficiency.

Frequently asked questions

Cortisol varies several-fold across the day, peaking in the morning and reaching a nadir at night. A single value can be normal yet mask loss of the evening nadir or a flattened rhythm, both important for diagnosing Cushing syndrome and characterising HPA axis dysregulation.

How to access the Cortisol × 4 test

The Cortisol × 4 reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.

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About this page

Published: October 7, 2026

Last reviewed: October 7, 2026

References:

Nieman LK, et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2008)
Bornstein SR, et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2016)
Clow A, et al. The cortisol awakening response: more than a measure of HPA axis function. Neurosci Biobehav Rev. (2010)
Adam EK, et al. Diurnal cortisol slopes and mental and physical health outcomes: a systematic review and meta-analysis. Psychoneuroendocrinology. (2017)
Raff H, et al. Late-night salivary cortisol as a screening test for Cushing's syndrome. J Clin Endocrinol Metab. (2009)

This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.