Single marker guide · Cortisol (stress hormone)
Cortisol is the hormone that gets you out of bed, and the one that keeps you awake at 3am when life is too much. A blood test can show whether your stress system is overworked, exhausted or running normally, but only if it is taken at the right time of day and read against the hormones it pushes around. Most cortisol tests fail on both counts.
Morning venous draw at 103 UK clinics or at home. UKAS-accredited laboratory. Report reviewed by a medical professional.
The short answer
Cortisol follows a steep daily curve: it peaks within an hour of waking, falls through the day, and bottoms out around midnight. A reading of 250 nmol/L is perfectly healthy at 8am and alarmingly high at 11pm. That is why a cortisol result without a time on it is close to worthless, and why every TrueVitals cortisol is drawn in the morning, fasted, at the top of the curve where the reference range actually applies.
The second thing to know is that cortisol never acts alone. It suppresses testosterone, blunts thyroid conversion, drives blood sugar and insulin up, raises blood pressure and breaks down muscle. So the question "is my cortisol high?" is really "what is my cortisol doing to everything else?", and the answer lives in DHEA-S, testosterone, Free T3, fasting insulin and blood pressure. One number tells you where you are on the curve. The rest tell you what it is costing you.
Reference ranges
| 8 to 9am serum cortisol | Category | What it means |
|---|---|---|
| Below 100 nmol/L | Low | Possible adrenal insufficiency. Not a lifestyle finding: see your GP promptly for a short synacthen test. Sodium, potassium and blood pressure in the same panel add important context. |
| 100 to 165 nmol/L | Borderline low | Below the reference range. Can follow steroid inhalers or creams, recent illness, or sampling later than 9am. Worth repeating at the right time and discussing with your GP if it persists. |
| 166 to 507 nmol/L | Reference range | A normal morning peak. Where you sit within this band, and what DHEA-S and testosterone are doing beside it, is where the useful information is. |
| 507 to 600 nmol/L | High-normal | Common in people under sustained pressure, sleeping badly, or training very hard. Also seen with the combined pill and HRT, which raise the protein cortisol binds to and inflate the total. |
| Above 600 nmol/L | High | If accompanied by central weight gain, easy bruising, raised blood pressure or high blood sugar, your GP may arrange further testing to rule out Cushing's. Often it is acute stress, illness or medication, and repeats normally. |
Laboratory ranges vary; some run 133 to 537 nmol/L. Serum cortisol measures total cortisol, most of which is bound to a carrier protein. Oestrogen-containing contraception and HRT raise that protein, so women taking them often read high without any excess of active hormone. TrueVitals reports account for this when you tell us your medication.
Symptoms
A healthy rhythm gives you a surge on waking and a slide by evening. Chronic stress flattens it: you drag yourself up, then find a second wind at 10pm and lie awake with your mind racing. That inverted pattern is the most common cortisol complaint in working adults. Stress blood test guide.
Cortisol tells the body to store fat centrally and to release glucose, which drives insulin up. Belly fat that will not shift despite a good diet, plus cravings for sugar and salt, is a stress-hormone signature. Can't lose weight guide.
The body makes cortisol and testosterone from the same raw material and prioritises survival over reproduction. Sustained high cortisol suppresses testosterone in men and women alike. Testing one without the other misses the connection. Low libido blood test guide.
Cortisol keeps the brain on alert. Too much for too long produces a constant background hum of anxiety, snappiness, and trouble concentrating that is easy to mistake for a purely psychological problem. Anxiety blood test guide.
Cortisol is an immune suppressant. Frequent colds, slow wound healing, and flare-ups of skin conditions or cold sores under pressure all point to a stress system that has been running hot.
The other direction. Genuinely low cortisol causes profound fatigue, light-headedness on standing, nausea, weight loss and salt cravings, sometimes with darkening skin. It is rare and it is a medical emergency in the making, which is why a low morning result goes straight to your GP.
Straight talk
You will find plenty of sites that will diagnose adrenal fatigue from a cortisol result and sell you a supplement for it. Adrenal fatigue is not a recognised medical condition, and the research does not support the idea that ordinary stress wears the adrenal glands out. What chronic stress does do is flatten the daily rhythm and keep cortisol inappropriately high in the evening, which is a different problem with different fixes: sleep, training load, caffeine timing, and in some cases addressing the thyroid or blood sugar problems cortisol has created.
A genuinely low morning cortisol, on the other hand, is not fatigue. It can be adrenal insufficiency, which needs proper investigation and treatment from your GP, and it can also be the after-effect of steroid inhalers, creams or tablets that have quietly suppressed your own production. A TrueVitals report tells you which of these your result looks like, rather than reaching for the label that sells.
Read it in context
Cortisol on its own tells you where you sit on the morning curve. Read alongside the right markers, it tells you what your stress system is doing to your hormones, your metabolism and your recovery.
The adrenal glands' other main hormone and cortisol's natural counterweight. Under long-term stress cortisol stays up while DHEA-S drifts down, and the ratio between them is a better read on strain than either alone. Both are in every TrueVitals panel.
Cortisol suppresses testosterone directly. High-normal cortisol with low-normal testosterone in a man in his thirties is stress showing up as a hormone problem, and it is far more common than a primary testicular issue. Testosterone blood test guide.
Cortisol slows the conversion of inactive T4 into active T3, so chronic stress can produce thyroid symptoms with a normal TSH. Only a panel with Free T3 can see it. Thyroid blood test guide.
Cortisol raises blood glucose by design. Sustained, that drives insulin resistance years before diabetes appears. A high-normal cortisol with a rising HOMA-IR is the earliest metabolic warning most people will ever get. Insulin and HOMA-IR are in the Ultimate panel. Prediabetes guide.
Low sodium with high potassium alongside a low cortisol strengthens the case for adrenal insufficiency and makes the GP conversation urgent. A raised CRP with high cortisol points to inflammation as the stressor rather than lifestyle.
Because exhaustion is the presenting symptom, the panel needs to rule out the simpler explanations at the same draw: iron stores, B12, thyroid. Chasing cortisol while your ferritin sits at 12 is how people stay tired for years. Ferritin blood test guide.
Which test
Advanced
74 biomarkers · £269
Cortisol and DHEA-S with testosterone and SHBG, full thyroid including Free T3, HbA1c, sodium and potassium, hs-CRP, full iron studies, B12, vitamin D, liver and lipids. The right choice if stress, sleep or burnout is the question.
View AdvancedMost chosen
Ultimate
114 biomarkers · £349
Everything in Advanced plus fasting insulin and HOMA-IR, the complete hormone set including oestradiol, LH, FSH and prolactin, Lp(a), immunoglobulins and urinalysis. The panel that shows what cortisol is doing to your metabolism, not just your mood.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. Extended cardiovascular, metabolic syndrome, autoimmune and neurological screening on top of everything above. The deepest private panel in the UK.
View SignatureMorning appointments available. Clinic draw £19 at 103 UK clinics. At-home phlebotomist £39 across 200+ areas. Fast from 10pm the night before. Pay monthly available.
Honest comparison
If your specific question is the shape of your daily rhythm, a four-point saliva cortisol test, sampled on waking, at noon, in the afternoon and at bedtime, shows the curve in a way a single blood draw cannot. They cost around £80 to £150 from specialist labs and are the right tool for that question. Equally, if your GP suspects Cushing's or Addison's, the dynamic tests they arrange are the correct route and no private panel replaces them.
A morning blood cortisol inside a full panel is the better choice when you want to know whether stress is the reason you feel the way you do, because that answer lives in what cortisol is doing to testosterone, thyroid, insulin and the rest, not in cortisol alone. A standalone cortisol blood test costs around £39 to £49 elsewhere; the Advanced panel is £269 for cortisol with 73 markers of context, a venous draw and a fully written report. See how every UK provider compares.
After the result
Book a GP appointment this week and take your report. If you use any steroid medication, including inhalers and skin creams, say so: it is the most common cause and it matters. Your report flags this result clearly and tells you what to ask for.
The levers that move cortisol are unglamorous and they work: a fixed wake time, daylight within an hour of waking, no caffeine after noon, training hard but not every day, and protecting seven hours of sleep. Your report shows which downstream markers are already affected, which tells you how urgent this is.
Cortisol responds to changes in weeks, and so do the hormones it suppresses. A morning retest shows whether cortisol has settled and whether testosterone, Free T3 and insulin have recovered with it. Your second report compares against your first automatically.
This page is general information, not medical advice. If you have severe fatigue with dizziness, vomiting or confusion, seek urgent medical care: these can be signs of an adrenal crisis.
FAQs
Total cortisol in serum, reported in nmol/L, at the moment the sample is taken. Because cortisol peaks after waking and falls through the day, the result only means something when compared with the range for that time. TrueVitals draws cortisol between 8 and 9am where the morning reference range applies.
Typical 8 to 9am reference ranges run around 166 to 507 nmol/L, with some laboratories quoting 133 to 537. Levels below 100 in the morning need GP follow-up, and levels well above the range with symptoms may prompt further testing. Afternoon and evening values are much lower and have their own ranges.
Between 8 and 9am, ideally within an hour or two of waking, on a normal day. Book a morning appointment, avoid intense exercise beforehand, and take any steroid medication after the draw unless your doctor has said otherwise. TrueVitals asks you to fast from 10pm the night before for the rest of the panel.
Yes. Oestrogen raises the level of the protein that carries cortisol in the blood, so total cortisol reads higher without any real excess. Women on the combined pill or oral HRT often sit above the reference range for this reason. Tell us your medication and the report interprets the result accordingly.
Not as a single number, but its effects do. Sustained stress typically produces a high-normal morning cortisol with a low-normal DHEA-S, suppressed testosterone, a lower Free T3, rising fasting insulin, and often a raised CRP. Seeing that pattern across a panel is far more informative than a lone cortisol value, which is why we test it in context.
It is not a recognised medical diagnosis and the evidence does not support ordinary stress exhausting the adrenal glands. Chronic stress flattens the cortisol rhythm rather than draining it. A genuinely low morning cortisol has real medical causes, principally adrenal insufficiency or steroid medication, and needs proper investigation rather than a supplement.
Yes, if your GP suspects a specific disorder such as Addison's or Cushing's. GPs rarely test cortisol for stress or tiredness alone. If you want to understand what stress is doing to your hormones and metabolism, a private morning panel is the direct route. What to ask your GP for.
A standalone cortisol blood test is around £39 to £49, and a four-point saliva rhythm test around £80 to £150. A TrueVitals Advanced panel is £269 and includes morning cortisol with DHEA-S, testosterone, full thyroid, HbA1c and 68 other markers, with a venous draw and a fully written report.
74 to 230 biomarkers. Morning venous draw at 103 UK clinics or at home. A report that tells you what your results mean and what to do next.
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