hormones · 1 min read
Cortisol test explained: blood, saliva and urine
A cortisol test means little without the clock: cortisol swings hour to hour, so a single blood draw is nearly meaningless on its own. Here is which test, blood, saliva or urine, answers which question.
Written by Lifebar Desk · Checked against the sources listed below
Published 16 Aug 2026
Key takeaways
- Cortisol peaks 30 to 45 minutes after waking and falls through the day, so timing defines the result.
- Late-night salivary cortisol and 24-hour urinary free cortisol are the screening tests for Cushing's syndrome.
- Direct-to-consumer "adrenal fatigue" panels are not a recognised diagnostic tool.
Cortisol follows a steep daily curve. Any test that ignores the clock is measuring noise.
The curve
Levels rise sharply in the hour before waking, peak 30 to 45 minutes after you open your eyes, the cortisol awakening response, then decline across the day to a trough around midnight. A value that is normal at 8am would be abnormal at 11pm.
The tests
| Test | Measures | Best used for |
|---|---|---|
| Morning serum | Point-in-time total cortisol | Adrenal insufficiency screening, with ACTH |
| Late-night salivary | Free cortisol at the trough | Cushing's syndrome screening |
| 24-hour urinary free cortisol | Total daily output | Cushing's syndrome screening |
| Dexamethasone suppression | Feedback response | Confirming excess production |
Why one blood draw disappoints
Acute stress, a needle, traffic, a rushed appointment, raises cortisol within minutes. So does illness, pregnancy, oral contraceptives and shift work. A single elevated reading in isolation rarely means anything.
Direct-to-consumer panels
Four-point saliva tests marketed for "adrenal fatigue" produce a curve that looks scientific and has no validated interpretation for that purpose. A 2016 systematic review of 58 studies found no substantiation for adrenal fatigue as a condition.
If your symptoms are fatigue, poor sleep and low mood, the productive path is evaluating sleep, thyroid function, iron, B12, and depression, not a cortisol curve.
Frequently asked
What is a normal morning cortisol?
Laboratory ranges vary, commonly around 6 to 23 mcg/dL for a morning serum draw. Interpretation depends on the exact time and the lab's own reference interval.
Is adrenal fatigue a real diagnosis?
No. Systematic reviews found no consistent evidence for it, and endocrine societies do not recognise it. The symptoms are real; the proposed mechanism is not supported.
Sources
Educational content, talk to your clinician before changing treatment.
