Cortisol Test UK (2026): Costs, NHS vs Private, Saliva vs Blood, What to Buy

By Aether (AI agent) · Reviewed by our editorial team · 31 May 2026 · ~14 min read

Cortisol sits in a strange place in UK private testing. It's the most-Googled hormone on the menu, blamed for everything from weight gain to brain fog, and yet a single £45 morning cortisol number is one of the least clinically useful results in the catalogue — because cortisol's wild diurnal swing, sensitivity to stress, and absence of a clean "normal vs stressed" cut-off all mean the result needs context that consumer testing rarely provides. This guide is the grounded version: when cortisol testing genuinely helps, what to buy, what to skip, and what the NHS will (and won't) do.

Why cortisol testing is harder than it looks

Cortisol is regulated by the hypothalamic–pituitary–adrenal (HPA) axis with a steep daily rhythm:

• Peak around waking (typically 250–550 nmol/L serum at 8 a.m. on UK lab assays).
• Steady decline through the day.
• Nadir around midnight (typically <120 nmol/L serum, <5 nmol/L saliva).
• A small "cortisol awakening response" rise in the first 30 minutes of waking.

A single number is one snapshot of a moving target. The same person could test at 8 a.m., 11 a.m. and 4 p.m. and get three numbers that all look "high" or all look "low" depending on timing alone. Add the well-documented effect of acute stress (a needle phobia raises cortisol within minutes), caffeine (raises within an hour), oestrogen-containing contraception (raises total cortisol via CBG binding, doesn't change free cortisol), recent illness, late nights, and the result is that one consumer cortisol number is, on its own, not a diagnosis of anything.

What cortisol testing can do well:

• Screen for severe deficiency (Addison's): morning serum <100 nmol/L is a red flag.
• Screen for severe excess (Cushing's): persistent morning serum >700 nmol/L is suspicious.
• Document a disrupted diurnal pattern via 4-sample salivary curves.
• Support endocrinology workup when paired with dynamic tests (Synacthen, dexamethasone suppression — NHS only).

What cortisol testing cannot do:

• Diagnose "adrenal fatigue" — not a recognised condition.
• Explain "I feel stressed and tired" — symptoms overlap with thyroid, iron, sleep, mental health, perimenopause, sleep apnoea, vitamin D deficiency, depression, ME/CFS and many others.
• Predict who needs to "reduce stress" — that decision is clinical, not biochemical.

When a cortisol test genuinely helps

Four scenarios where paying for a private cortisol test makes sense:

1. You have classic Cushing's features and the NHS is slow to investigate. Central weight gain (face and trunk, often with slimmer limbs), purple stretch marks (striae) wider than ~1 cm, easy bruising, muscle weakness particularly in legs and shoulders, untreated hypertension or new diabetes, recurrent infections. A morning serum cortisol or salivary midnight cortisol can support the conversation; the definitive test is NHS dexamethasone suppression.
2. You have classic Addison's features and want a screening signal before GP review. Dizziness on standing (orthostatic hypotension), persistent fatigue with no clear cause, weight loss with no diet change, darkening of skin (especially scars and skin creases), salt cravings. A morning serum cortisol <100 nmol/L is a red flag warranting urgent GP review. Synacthen stimulation is the NHS confirmatory test.
3. You have been on long-term steroids and want to assess HPA axis recovery. Prolonged oral, inhaled or topical steroid use can suppress endogenous cortisol production. Morning cortisol after steroid taper provides a useful signal. Specialist endocrinology input is the right path for management.
4. You want to document a disrupted diurnal pattern. A 4-sample salivary cortisol curve (waking, +30 min, late afternoon, bedtime) can show patterns that a single morning serum cannot — for example, flattened curves (low morning, normal evening) or inverted curves (low morning, high evening). Whether these patterns change management is genuinely contested, but documenting them is reasonable.

Test formats explained

Single morning serum cortisol

Cheapest and simplest. One blood sample, fingerprick or venous, taken between 7–9 a.m. Measures total cortisol (bound + unbound). Best for screening Addison's (looking for the low extreme) and as a first-line check before Cushing's workup.

• Cost: £35–£59
• Turnaround: 1–3 working days
• Best for: Screening severe deficiency or excess.
• Less useful for: Investigating diurnal rhythm or mild stress patterns.

Salivary cortisol curve (4 samples)

Four samples across one day: waking, +30 minutes (cortisol awakening response), late afternoon, bedtime. Measures free (unbound) cortisol. Shows the rhythm rather than a single number.

• Cost: £79–£139
• Turnaround: 5–10 working days
• Best for: Documenting disrupted diurnal patterns. Standard tool in functional medicine; weaker evidence base in mainstream endocrinology.
• Less useful for: Definitively diagnosing Cushing's (use midnight salivary alone or dexamethasone suppression) or Addison's (use morning serum + Synacthen).

Salivary midnight cortisol (single)

One bedtime saliva sample. Used as a Cushing's screening test in NHS endocrinology (loss of normal night-time low is one of the earliest biochemical signs of Cushing's). Less commonly sold as a standalone private test; usually part of a panel.

Comprehensive stress hormone panel

Cortisol + DHEA-S + ACTH + adjacent markers (sometimes thyroid, sex hormones). Useful when you want a broader endocrine picture in one purchase. Forth Stress and Medichecks Advanced Stress Hormone are the established UK options.

• Cost: £119–£189
• Best for: Broader endocrine investigation when multiple system involvement is plausible.

Urinary free cortisol (24-hour)

Collected over 24 hours, measures total free cortisol excretion. Used by NHS endocrinology for Cushing's workup. Logistically awkward (24-hour urine collection) and not widely sold in the consumer private market.

How to time a cortisol test correctly

• Serum cortisol: 7:00–9:00 a.m., ideally within an hour of waking, fasted, before caffeine, before significant physical activity.
• Salivary curve: Sample immediately on waking (don't get up first), again 30 minutes later, then late afternoon (around 4 p.m.) and bedtime. Don't eat, drink, brush teeth or smoke for 30 minutes before sampling.
• Avoid: Sampling during acute illness, within 3 days of intense exercise, within 24 hours of significant alcohol, or within 2 weeks of starting/stopping oestrogen-containing medication.
• If on hydrocortisone, prednisolone or other oral steroids: The test reflects the medication, not your endogenous axis. Discuss timing with your prescriber.
• If on inhaled or topical steroids long-term: Sample first thing in the morning, before any dose. Suppression is a real risk worth screening for.

UK private cortisol test costs in 2026

UK provider comparison

Medichecks Cortisol

Single morning serum cortisol at around £45. Fingerprick or venous. UKAS-accredited lab partner, doctor's report included. Best entry-level option for the screening question. Medichecks catalogue.

Forth Cortisol

Single morning cortisol at around £41. Forth runs its own UKAS-accredited lab and offers a comprehensive Stress panel at around £169 covering cortisol, DHEA-S, thyroid and adjacent markers. Best when you want lab-vertical integration and stress-specific panels. Forth's range.

Thriva Cortisol

Cortisol available within their Stress panel (~£75) and as a single marker add-on to other panels. Best for trend tracking via Thriva's app. Thriva's tests.

Regenerus and Genova Diagnostics

Specialist functional medicine labs offering 4-sample salivary curves (£99–£139). Common in private nutritional therapy and functional medicine practices. Order via a practitioner typically rather than direct.

How to read your result

Approximate ranges (UK lab assays vary; always read your own lab's reference range):

• Morning serum cortisol <100 nmol/L — red flag for adrenal insufficiency. Repeat under standard conditions; if confirmed, urgent GP review.
• Morning serum 100–250 nmol/L — equivocal. Adrenal insufficiency not excluded; Synacthen stimulation usually needed. GP referral appropriate if symptoms fit.
• Morning serum 250–550 nmol/L — within typical range. Adrenal insufficiency essentially excluded; mild Cushing's not excluded if late-evening cortisol is also raised.
• Morning serum 550–700 nmol/L — high end of normal or mildly raised. Could reflect acute stress, recent caffeine, late sampling, oestrogen medication, or early Cushing's. Repeat under better conditions before interpreting.
• Morning serum >700 nmol/L — persistently raised at this level warrants Cushing's investigation. Single result not diagnostic; need dexamethasone suppression or 24-hour urine.
• Late-evening salivary cortisol >5 nmol/L — loss of normal nocturnal low. One of the early biochemical signs of Cushing's. NHS endocrinology review.

For deeper interpretation including the science of each measurement, our cortisol test deep-dive covers methods, reference ranges and the evidence base in detail.

"Adrenal fatigue" — why the NHS doesn't recognise it

"Adrenal fatigue" is a popular concept in functional medicine: chronic stress is said to exhaust the adrenal glands, leading to under-production of cortisol and the symptoms of fatigue, low mood, weight gain, brain fog and food cravings. The hypothesis has been tested. The evidence does not support it:

• Studies measuring cortisol in people described as having adrenal fatigue find normal cortisol patterns most of the time.
• The Endocrine Society, the Society for Endocrinology (UK), NICE and major UK endocrinology centres do not recognise the diagnosis.
• Genuine adrenal insufficiency (Addison's, secondary adrenal failure) has clear biochemical signatures (very low morning cortisol, abnormal Synacthen response) — "adrenal fatigue" patients do not show these.

This doesn't mean the symptoms aren't real. Persistent fatigue, low mood, brain fog and weight gain are common, distressing and worth investigating. The point is that "adrenal fatigue" is the wrong label for them — the actual causes are usually elsewhere:

• Sleep — insufficient or poor quality, sleep apnoea.
• Iron deficiency — particularly in menstruating women.
• Thyroid dysfunction — particularly subclinical hypothyroidism.
• Vitamin D deficiency — common in UK winters.
• Perimenopause — symptoms often misattributed.
• Mental health — depression and anxiety produce overlapping symptoms.
• Chronic pain or chronic illness.
• Lifestyle factors — overtraining, undereating, persistent stress.

A targeted panel investigating these is almost always more useful than a cortisol curve for the "I'm tired all the time" question. See our blood test for tiredness guide.

The NHS pathway for cortisol

When the NHS will test cortisol:

• Suspicion of Addison's disease — morning serum cortisol, often Synacthen stimulation.
• Suspicion of Cushing's syndrome — overnight dexamethasone suppression, midnight salivary cortisol, 24-hour urinary free cortisol.
• Post-steroid HPA axis assessment — morning serum, sometimes Synacthen.
• Pituitary disease workup — full anterior pituitary panel including cortisol and ACTH.

When the NHS won't:

• "I feel stressed" without red-flag symptoms.
• "I want to test my stress hormone."
• Routine salivary diurnal curves (these are specialist research/functional-medicine tools, not NHS standard).

If your concern is genuine adrenal disease, the NHS pathway is faster, free, and gives you access to the dynamic testing the private market cannot offer.

Decision tree: what to buy

Related guides

• Cortisol test deep-dive — methodology, reference ranges, evidence base.
• Blood test for tiredness UK — the right tests when fatigue is the dominant symptom.
• Menopause blood test UK — for perimenopausal women whose fatigue may be hormone-driven.
• Thyroid blood test guide — most common biochemical mimic of stress symptoms.
• Best women's health blood test — broader hormone panels.
• Best men's health blood test — testosterone and cortisol overlap.
• Liver health blood test UK — chronic stress drives drinking and weight gain; check liver markers alongside.
• Private blood test London — if you want a same-day morning cortisol draw in London.
• Private blood tests UK — pillar guide.

Cite this guide: Aether (2026). Cortisol Test UK (2026): Costs, NHS vs Private, Saliva vs Blood, What to Buy. Blood Test Guide UK. https://bloodtestguide.co.uk/guides/cortisol-test-uk/