Why the curve matters
Cortisol isn't a single number. It's a curve. Healthy cortisol peaks 30 minutes after waking, declines through the day, reaches nadir at midnight, then rises again in early morning. Chronic stress and HPA axis dysfunction don't always raise the average, they often flatten or shift the curve. A single measurement at one time of day misses this.
Morning serum cortisol
What it measures: A single blood draw, ideally between 7 and 9 AM, at the natural cortisol peak.
Best for: ruling out severe adrenal insufficiency (Addison's disease) or extreme overproduction (Cushing's syndrome).
Limitations: A single point gives no information about the daily curve. Many people with chronic stress patterns show normal AM serum cortisol while having abnormal curves.
Optimal range: 10-18 µg/dL (drawn 7-9 AM).
4-point salivary cortisol
What it measures: Cortisol in saliva at four time points: waking, ~30 min after waking, noon, and bedtime. Some panels add a 4 PM point.
Best for: evaluating diurnal rhythm, chronic stress, burnout, sleep complaints, fatigue with normal AM serum.
Why salivary: measures free (bioactive) cortisol, not bound. Non-invasive (no needles). Catches morning cortisol awakening response.
Patterns to look for:
- Healthy: high morning, declining through day, low at bedtime
- Burnout pattern: flattened curve, elevated evening cortisol
- HPA dysfunction: blunted morning rise, elevated bedtime
- Cushing-like: high throughout, no nadir
Hair cortisol
What it measures: Cortisol deposited in hair shaft over preceding ~90 days.
Best for: chronic stress evaluation, retrospective look at the past 3 months. Useful for research and when you want a long-term average.
Limitations: doesn't show the curve or recent changes. Less commonly available.
24-hour urinary free cortisol
What it measures: Total free cortisol excreted over 24 hours.
Best for: ruling out Cushing's syndrome.
Limitations: hard to do correctly (must collect everything for 24 hours), shows total but not the curve.
Which test, when
| Goal | Best test |
|---|---|
| Ruling out severe adrenal disease | AM serum + ACTH |
| Evaluating chronic stress / burnout | 4-point salivary |
| Investigating sleep issues + cortisol | 4-point salivary (especially evening) |
| Looking back over 3 months | Hair cortisol |
| Suspected Cushing's | 24-hr urinary free + dexamethasone suppression |
| Routine screening | AM serum (with full hormone panel) |
The clinical pearl: "My cortisol is normal" usually means morning serum was in range, which doesn't rule out the chronic stress patterns most adults are actually concerned about.
Bottom line
Cortisol testing is more nuanced than a single number. For chronic stress, burnout, and HPA function, the 4-point salivary curve is the right test. AM serum is fine for screening but inadequate for the patterns most adults are investigating. Picking the right test up front saves time and gives a clearer picture.