Cortisol Blood Tests: Stress Hormone Testing Guide
Feeling constantly tired, struggling to sleep, or noticing unexplained weight gain around your middle? You might be quick to blame stress, but there’s a biological reason behind those feelings, and it has a name: cortisol.
Cortisol is your body’s primary stress hormone, produced by the adrenal glands. It’s responsible for your “fight or flight” response, regulating your metabolism, controlling your sleep-wake cycle, and managing inflammation. When it’s working properly, cortisol peaks in the morning to wake you up and gradually declines through the day so you can sleep. But when that rhythm gets disrupted, whether by chronic stress, poor sleep, or underlying health conditions, your health can suffer in ways you might not expect.
A simple blood test can measure your cortisol levels and give you a clear picture of what’s going on inside your body.
What a Cortisol Blood Test Measures
A cortisol blood test measures the concentration of cortisol in your bloodstream at a specific point in time. Unlike many other blood tests, the timing matters. Cortisol follows a natural daily rhythm called the diurnal cycle:
- Early morning (6–9am): Cortisol peaks, typically between 140–700 nmol/L. This is your body’s natural alarm clock.
- Midday: Levels drop to roughly half of your morning peak.
- Evening: Cortisol reaches its lowest point, usually below 50 nmol/L, to allow your body to wind down for sleep.
Because of this rhythm, the standard cortisol blood test is taken in the morning (around 9am) to get a baseline reading. Some providers also offer saliva tests at multiple points throughout the day for a more complete picture of your cortisol rhythm.
Signs You Might Need a Cortisol Test
Cortisol imbalances can show up in many ways. High cortisol (hypercortisolism) is often linked to chronic stress, while low cortisol (adrenal insufficiency) can leave you feeling drained and unable to cope.
Symptoms of high cortisol may include:
- Persistent fatigue despite getting enough sleep
- Weight gain, especially around the abdomen and face (“moon face”)
- High blood pressure
- Mood swings, anxiety, or irritability
- Poor sleep quality or waking up feeling unrested
- Brain fog and difficulty concentrating
- Weakened immune system, so you get sick more often
- Muscle weakness
Symptoms of low cortisol (adrenal insufficiency) may include:
- Extreme fatigue that doesn’t improve with rest
- Unexplained weight loss
- Low blood pressure (feeling dizzy when standing up)
- Salt cravings
- Darkening of the skin
- Digestive issues
If several of these symptoms sound familiar, a cortisol blood test can help you understand whether your stress hormone levels are within a healthy range.
NHS vs. Private Cortisol Testing
Getting a cortisol test on the NHS is possible, but it usually requires a GP referral and a clear clinical reason, such as suspected Cushing’s syndrome (high cortisol) or Addison’s disease (low cortisol). If you’re simply feeling burnt out or stressed, the NHS may not consider testing a priority.
Private testing offers a much simpler route. You can order a cortisol test online, provide a finger-prick or venous blood sample from home or at a clinic, and receive your results within days, with reference ranges so you can understand where your levels sit.
To compare cortisol and stress hormone test prices across all providers, visit our compare page to look at cortisol tests.
How Much Does a Private Cortisol Test Cost?
| Provider | Test | Price | Link |
|---|---|---|---|
| Forth | Cortisol Home Blood Test Kit | £41 | View test |
| Medichecks | Cortisol (9am) Blood Test | £45 | View test |
| Medichecks | Testosterone & Cortisol Blood Test | £72 | View test |
Forth offers the cheapest standalone cortisol test at £41, while Medichecks is close behind at £45 for their morning cortisol test. If you also want to check your testosterone levels, which can be affected by chronic stress, Medichecks offers a combined Testosterone & Cortisol test for £72.
What About Bundled Health Checks?
Cortisol is also included in many broader health panels:
- Forth includes cortisol in their Female Hormone Imbalance Test (£89) and Male Hormone Blood Test (£89)
- Medichecks includes cortisol in several hormone panels like the Male Hormone Check (£79) and Female Hormone Check Advanced (£99)
- Numan includes cortisol in their Essential Hormone Analysis (£68) for men
If you’re already planning a comprehensive health check-up, adding cortisol to a broader hormone panel can give you better context than testing it alone.
Understanding Your Results
When you get your cortisol test results, you’ll see a reference range that looks something like this:
| Time | Normal Range (approximate) |
|---|---|
| 9am sample | 140–700 nmol/L |
| 4pm sample | 80–350 nmol/L (if tested) |
High cortisol may indicate Cushing’s syndrome, chronic stress, or certain medications (like corticosteroids or the contraceptive pill). If your levels are significantly elevated, your GP may recommend further testing, including a dexamethasone suppression test or 24-hour urine collection.
Low cortisol may indicate adrenal insufficiency (Addison’s disease), a pituitary gland problem, or the effects of long-term steroid medication. This is a serious condition that requires medical attention.
It’s important to remember that a single result outside the normal range doesn’t necessarily mean something is wrong. Cortisol levels fluctuate naturally, and factors like recent exercise, illness, poor sleep, or even the stress of having blood drawn can temporarily affect your levels. Your GP will usually recommend a repeat test to confirm any abnormal result.
How to Prepare for a Cortisol Test
Getting accurate results from a cortisol blood test depends on good preparation.
Book a morning appointment between 8am and 10am, when levels are highest, and avoid vigorous exercise for the 24 hours beforehand, since intense workouts can spike cortisol temporarily. Get a good night’s sleep (sleep deprivation can significantly elevate cortisol) and skip alcohol the night before, as it can interfere with cortisol production.
Tell your doctor about any medications: birth control pills, corticosteroids, and some antidepressants can affect cortisol levels. And try not to stress about the test itself. In my experience the hardest instruction here is the last one, because the anxiety of having blood taken can briefly raise your reading.
What to Do If Your Results Are Abnormal
If your cortisol test comes back outside the normal range, here’s what you can do.
If your cortisol is high, start with stress management: meditation, deep breathing, and gentle exercise like yoga can help lower cortisol naturally, and even 10 minutes a day makes a difference. Prioritise sleep, aiming for 7–9 hours of quality rest, with less screen time an hour before bed and a cool, dark bedroom. Cut back on caffeine, which stimulates cortisol production; switching to herbal teas or limiting coffee to one cup before midday helps. Eat a balanced diet, reducing sugar and processed foods, which can spike cortisol, in favour of whole foods, healthy fats, and plenty of vegetables. Adaptogenic herbs such as ashwagandha, rhodiola, and holy basil have shown promise in helping regulate cortisol levels, but talk to a qualified herbalist or nutritional therapist before taking supplements.
If your cortisol is low, see your GP first. Low cortisol can indicate adrenal insufficiency, which requires medical investigation, so don’t try to self-treat. Eat regularly rather than skipping meals, since low blood sugar can worsen symptoms of adrenal insufficiency; small, frequent meals with protein and healthy fats work well. Reduce stress where you can and cut back on demanding commitments, because your adrenal glands need rest. And if you’ve been on long-term steroid medication, you may need a gradual reduction under medical supervision: never stop steroids suddenly.
Header image from Pexels
Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a GP or qualified healthcare provider before making decisions about your health.