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What is a cortisol test?
Cortisol tests measure the level of cortisol — your body's primary stress hormone — in your system. But not all cortisol tests are measuring the same thing, and choosing the wrong type can leave you with a result that tells you very little.
This page explains the different types of cortisol test, what each one can and can't tell you, and why the sample type matters as much as the result.
What is cortisol and why does it matter?
Cortisol is produced by the adrenal glands in response to stress, but it does far more than manage your stress response. It regulates metabolism, immune function, blood pressure, sleep cycles, reproductive hormones, and brain function. Every cell in the body has cortisol receptors — which is why sustained imbalance, whether too high or too low, can produce a wide range of symptoms affecting almost every system.
Short-term cortisol spikes are normal and necessary. The problem is when cortisol is chronically elevated or chronically suppressed over weeks and months — patterns that a single snapshot test can easily miss.
Types of cortisol test
Blood cortisol test
The most common type, typically ordered by a GP. A blood sample is taken and analysed for cortisol concentration at that moment in time. Blood tests are most useful for diagnosing acute adrenal conditions (like Addison's or Cushing's) in a clinical setting, often combined with a stimulation test.
What it measures: Cortisol at one point in time — typically a morning sample.
Limitations: Cortisol peaks in the morning and drops throughout the day, so the result depends heavily on when the test is taken. It's also affected by acute stress, exercise, recent meals, and the anxiety of the blood draw itself. A high result might be a genuine abnormality — or it might just mean you had a stressful morning. A normal result doesn't tell you whether your cortisol has been elevated for the past three months.
Saliva cortisol test
Saliva tests measure free (unbound) cortisol and are often collected at multiple points across one day to map the diurnal rhythm. A late-night salivary cortisol test is a standard screening tool for Cushing's syndrome.
What it measures: Free cortisol at the time of collection. Multiple samples give a daily pattern.
Limitations: Results vary significantly depending on the time of day, stress levels, and collection technique. Like blood tests, they reflect a single day — not a sustained pattern over weeks or months. Repeated collections across multiple days improve accuracy but add complexity and cost.
Urine cortisol test (24-hour)
A 24-hour urine collection measures total cortisol output over a full day. It smooths out some of the hourly variation seen in blood and saliva tests, and is used in clinical investigation of adrenal conditions.
What it measures: Total free cortisol excreted over 24 hours.
Limitations: Still only represents a single day. Results can vary considerably between collection days, and the process requires careful, uninterrupted collection. It doesn't reveal whether cortisol has been consistently elevated or suppressed over a longer period.
Hair cortisol test
The most recent and most informative method. As hair grows (approximately 1cm per month), cortisol from the bloodstream is incorporated into the hair shaft. Analysing the section of hair closest to the scalp provides a reliable, averaged measure of cortisol exposure over the past three months — unaffected by what happened the morning of the test.
What it measures: Average cortisol over the past 3 months.
Advantages: Single sample. No timing requirements. Not affected by acute stress, exercise, or time of day. Validated by decades of peer-reviewed research at institutions including University of Oxford, King's College London, and Harvard. The only type of cortisol test that reliably reflects chronic (long-term) cortisol patterns.
Cortisol test types compared
Other cortisol tests only measure where your cortisol sits at a single moment. But cortisol changes minute by minute — which is why a one-off blood test can miss the full picture. Hair cortisol testing works like an HbA1c for blood sugar: it gives you a reliable average over three months, not just a snapshot of today.
| Feature | Hair test Cortigenix | Blood test | Saliva test | Urine test |
|---|---|---|---|---|
| Measures cortisol over 3 months | ✓ | ✗ | ✗ | ✗ |
| Single sample — no repeat testing needed | ✓ | ✗ | ✗ | ✗ |
| Unaffected by acute stress on test day | ✓ | ✗ | ✗ | ✗ |
| Detects chronic (long-term) cortisol patterns | ✓ | ✗ | ✗ | ✗ |
| No needles or clinic visit required | ✓ | ✗ | ✓ | ✓ |
| Suitable for at-home self-collection | ✓ | ✗ | ✓ | ✓ |
| Results unaffected by time of day | ✓ | ✗ | ✗ | ✗ |
| Validated by peer-reviewed research | ✓ | ✓ | ✓ | ✓ |
| Useful for diagnosing adrenal conditions | ✓ | ✓ | ✓ | ✗ |
Order your hair cortisol test – £126.75 RRP £169.00 — save 25%
Which cortisol test is right for you?
The right test depends on what you're trying to find out:
If you want to know whether chronic stress is affecting your health — a hair cortisol test is the only option that gives you a meaningful answer. Blood and saliva tests measure a single moment; hair tests measure the sustained pattern that actually drives long-term health outcomes.
If you're investigating a possible adrenal condition (Cushing's or Addison's) — your GP will typically start with blood and saliva tests as part of a clinical workup. A hair cortisol test can complement this, particularly for cyclical Cushing's where point-in-time tests often return false negatives during low phases.
If you're monitoring a known condition — hair testing is particularly valuable for tracking cortisol levels between clinical appointments, without the need for repeated blood draws or 24-hour urine collections.
If you're optimising for performance or longevity — hair testing provides the baseline and repeat measurement data needed to track whether lifestyle interventions are actually working.
What are you testing for?
Cortigenix's hair cortisol test is the same clinically-validated test regardless of your reason for testing. Choose the pathway most relevant to you for tailored guidance:
Choose your reason for testing
Choose what fits you best — it's the same clinically-validated test, with guidance tailored to your reason for testing.
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Frequently asked questions about cortisol testing
Can I get a cortisol test on the NHS?
Yes — your GP can request a blood cortisol test, typically as part of an investigation for suspected adrenal conditions. However, NHS cortisol tests are point-in-time blood measurements and are generally only offered if you present with symptoms that suggest a clinical condition. Hair cortisol testing, which provides a 3-month average, is not routinely available on the NHS and is currently only available privately.
What's a normal cortisol level?
Normal ranges vary depending on the type of test and the time of collection. For a morning blood test, typical cortisol is roughly 170–540 nmol/L. For hair cortisol, normal reference ranges are expressed in pg/mg (picograms per milligram of hair) and vary by laboratory. Cortigenix's results dashboard places your result in context against validated reference ranges and explains what your level means.
Is a hair cortisol test accurate?
Yes — hair cortisol testing is backed by decades of peer-reviewed research and is the most accurate method available for measuring long-term cortisol exposure. Unlike blood, saliva, and urine tests, which are highly sensitive to the conditions on the day of collection, hair cortisol reflects a stable, averaged reading that is not distorted by acute stress, time of day, or exercise. Cortigenix's test has been independently validated using data from thousands of participants.
Do I need a doctor's referral to take a cortisol test?
No. Cortigenix's hair cortisol test is available directly without a GP referral. You order online, collect your sample at home, and receive your results through a secure personal dashboard. If your results are outside the normal range, our cortisol experts are available to discuss findings and next steps.
How soon will I get my results?
Results are typically available within 10 working days of your sample arriving at our laboratory. You'll receive an email notification when they're ready.