Cortisol, 3 Specimens
The Cortisol, 3 Specimens test measures serum cortisol at morning, midday, and afternoon time-points to map the hormone's circadian rhythm. It screens for adrenal insufficiency and Cushing syndrome by documenting whether the expected morning peak and afternoon nadir are preserved, and supports assessment of HPA axis regulation in chronic stress and fatigue.
4
Biomarkers
Blood (serum)
Sample
2–3 business days
Turnaround
No
Fasting
What is the Cortisol 3-Point test?
The Cortisol, 3 Specimens test measures serum cortisol at three time-points across a single day — typically morning, midday, and afternoon — to map the hormone's physiological circadian rhythm. Cortisol is the principal glucocorticoid secreted by the adrenal cortex under ACTH drive, and its concentration normally peaks in the early morning and declines to a nadir in the evening. Disorders of cortisol excess or deficiency disrupt this pattern, so serial sampling offers more diagnostic information than a single random level. Practitioners order the three-specimen protocol to screen for adrenal insufficiency, to investigate suspected Cushing syndrome by documenting loss of the expected decline, and to assess HPA axis regulation in patients with chronic stress, fatigue, or symptoms that suggest dysregulated cortisol secretion. The test complements — but does not replace — dynamic function tests such as ACTH stimulation or low-dose dexamethasone suppression when a definitive diagnosis is required.
What does the Cortisol 3-Point test measure?
Cortisol exhibits a pronounced circadian rhythm, with peak secretion in the early morning driven by the hypothalamic-pituitary-adrenal axis. The morning specimen captures the zenith of physiological production, when intact axis function should yield the highest serum concentration.
The morning cortisol is the cornerstone of adrenal reserve screening. Values below 140 nmol/L raise suspicion for adrenal insufficiency, while marked elevation suggests Cushing syndrome or an acute stress response. Isolated morning values lack the temporal resolution to confirm cyclicity, which is why multi-point sampling is employed.
By midday, cortisol has declined from its morning peak but remains above nadir, reflecting the descending limb of the normal diurnal curve. The midday specimen documents this intermediate position.
Midday cortisol helps establish that the expected decline is occurring. A flat or inverted curve — midday values equal to or exceeding morning — can indicate loss of circadian rhythm, seen in some cases of Cushing syndrome or disrupted HPA regulation.
By mid-to-late afternoon, cortisol approaches its daily nadir, with secretion declining ahead of the evening trough. The afternoon specimen captures this lower physiological set-point.
The afternoon value completes the three-point curve and helps confirm that diurnal variation is preserved. In Cushing syndrome the afternoon cortisol often fails to suppress normally, while in adrenal insufficiency all time-points may be inappropriately low.
The pattern itself — a descending curve from 08:00 through 16:00 — is a marker of intact HPA axis regulation and circadian entrainment. Loss or flattening of the rhythm is a qualitative finding independent of absolute concentrations.
A preserved diurnal rhythm supports normal axis function, even if individual values fall at the edges of reference limits. A flat or inverted curve raises concern for endogenous hypercortisolism or, in the setting of chronic stress or shift work, HPA dysregulation.
Why is the Cortisol 3-Point test ordered?
- Screening for adrenal insufficiency in patients with unexplained fatigue, weight loss, hypotension, hyperpigmentation, or recurrent hypoglycaemia
- Investigation of suspected Cushing syndrome, where loss of the normal diurnal decline is an early feature and the three-point curve documents rhythm flattening
- Assessment of HPA axis regulation in chronic fatigue, burnout, or suspected 'adrenal dysregulation' in integrative and functional practice
- Evaluation of patients on long-term glucocorticoid therapy, to detect axis suppression and guide tapering or stress-dose coverage
- Follow-up of borderline morning cortisol results, where the diurnal pattern adds context to a single equivocal value
- Work-up of psychiatric or sleep disorders in which disrupted circadian cortisol rhythm is a recognised contributor
- Monitoring of shift workers or patients with circadian disruption, where flattening of the curve can reflect desynchronisation
- Paediatric evaluation of growth delay or adrenal disorders, interpreted with age-appropriate reference data
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
2–3 business days
Collection notes
Phlebotomy via Quest at three specified time-points: typically 08:00, 12:00, and 16:00 on the same day. Strict adherence to timing is critical; even minor delays alter the diurnal gradient. The patient should be seated and rested for at least 10 minutes before each draw to minimise stress-induced spikes. Avoid scheduling on days of acute illness, severe pain, or major stressors.
Specimen requirements
Minimum 0.5 mL serum per time-point (gel separator acceptable). Separate from cells promptly; cortisol is stable refrigerated for several days. Label each specimen clearly with the draw time. If the patient is on glucocorticoid therapy, note the drug, dose, and timing of the last dose.
What can affect Cortisol 3-Point results?
Cortisol's steep circadian gradient means that even a 30–60 minute deviation in draw time can shift results; strict adherence to 08:00, 12:00, and 16:00 (or the specified schedule) is essential for valid interpretation.
Pain, anxiety, venepuncture stress, or intercurrent illness can acutely raise cortisol at any time-point, potentially masking the diurnal decline or elevating all three values.
Oestrogen increases cortisol-binding globulin, raising total cortisol while free (active) cortisol may remain normal; consider free cortisol or salivary measurement in these contexts.
Exogenous glucocorticoids suppress endogenous cortisol; rifampicin and some antiepileptics induce cortisol metabolism; oral contraceptives raise binding globulin. A full medication history is mandatory.
Circadian misalignment and poor sleep can flatten the diurnal curve or phase-shift the rhythm, confounding interpretation.
Severe infection, surgery, or critical illness activate the HPA axis and can produce sustained cortisol elevation or loss of normal rhythm; interpretation must account for the clinical context.
What do Cortisol 3-Point results mean?
Elevated
All three specimens elevated with preserved or flattened rhythm: Cushing syndrome (endogenous hypercortisolism), exogenous glucocorticoid exposure, or acute severe stress. Flattened rhythm with high afternoon cortisol specifically suggests loss of circadian regulation seen in Cushing syndrome. Isolated morning elevation with normal decline may reflect a stress response or non-suppressed axis after steroid withdrawal.
Normal
Normal pattern: morning peak (≥350 nmol/L), midday intermediate, afternoon nadir, with a clear descending curve. This supports intact adrenal reserve and HPA axis regulation. However, a normal three-point curve does not exclude subtle rhythm disturbances detectable by salivary or multi-point testing, nor does it rule out intermittent hypercortisolism.
Reduced
All three specimens low or inappropriately flat at the low end: primary or secondary adrenal insufficiency. A morning cortisol below 140 nmol/L warrants dynamic testing (ACTH stimulation) to confirm the diagnosis. Low-normal values across the day in the setting of symptoms suggest partial insufficiency or HPA axis suppression from prior glucocorticoid use.
Note: Total serum cortisol measures both free and protein-bound hormone; oestrogen, pregnancy, and oral contraceptives elevate binding globulin and total cortisol without increasing bioactive free cortisol. In these settings, consider free cortisol (calculated or directly measured) or salivary cortisol. A single abnormal time-point requires correlation with symptoms and often repeat or dynamic testing. The diurnal pattern — the shape of the curve — is as important as absolute values, and a flat curve even within the reference range can be clinically significant. Stress at the time of draw can obscure true baseline function.
Frequently asked questions
Cortisol follows a steep circadian rhythm, peaking in the morning and declining to a nadir in the evening. Three time-points capture this pattern, revealing whether the diurnal curve is preserved, flattened, or inverted — information a single random value cannot provide.
How to access the Cortisol 3-Point test
The Cortisol 3-Point 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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Published: October 7, 2026
Last reviewed: October 7, 2026
- Bornstein SR, et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2016)
- Nieman LK, et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2008)
- Debono M, et al. Cortisol as a marker for increased mortality in patients with incidental adrenocortical adenomas. J Clin Endocrinol Metab. (2014)
- Raff H, et al. Physiological basis for the etiology, diagnosis, and treatment of adrenal disorders: Cushing's syndrome, adrenal insufficiency, and congenital adrenal hyperplasia. Compr Physiol. (2014)
- Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. (2016)
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.
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