What is measured
- Morning cortisol: the stress response hormone, taken at its daily peak
- DHEA-S: a second adrenal hormone that stays steady through the day
- The relationship between the two, read alongside thyroid and sex hormones where relevant
Cortisol follows a daily rhythm. It peaks in the first hour after waking and sits lowest around midnight. That is why the time of the draw changes the interpretation as much as the number itself.
How the test is done
Blood is drawn between 8 and 9 in the morning, because cortisol is judged at its daily peak.
Tell the doctor if you work night shifts, because your rhythm is shifted and the timing has to be adjusted. List every current medicine too. The contraceptive pill and estrogen therapy raise cortisol binding protein, so total blood cortisol can look high without the body being exposed to more active hormone.
DHEA-S is not tied to timing and can be taken in the same draw.
How results are read
One cortisol reading neither confirms nor rules out adrenal disease.
A genuine adrenal condition, over-active or under-active, is diagnosed with specific dynamic testing, not a single morning sample. If the first result raises that concern, the doctor refers you for the correct test rather than offering a half interpretation.
For most people who come in with fatigue, the value lies in ruling things out. A normal morning cortisol with a normal DHEA-S moves the conversation to the more common causes, which are sleep, iron, thyroid, blood sugar and actual workload.
