What it measures
Cortisol is a hormone made by the adrenal glands. It follows a daily rhythm, highest in the early morning and lowest around midnight, and rises with stress and illness. The blood test measures the total amount in serum.
Why people test it
- Measured when the adrenal glands may be making too little cortisol, as in Addison's disease.
- Measured when too much cortisol is suspected, as in Cushing's syndrome.
- Checked in people who have taken steroid medicines for a long time.
- Included in some private panels looking at tiredness and stress.
- Hard exercise raises cortisol for a few hours, which can show in a sample taken soon after training.
Typical range
Ranges vary by lab and method, and depend on the time of day the sample is taken. Oestrogen in the pill, HRT or pregnancy raises total cortisol. Your report shows the lab's own range, usually for a morning sample.
Finger-prick or vein?
A vein sample is usually advised. Hormone results from finger-prick samples can be affected by creams or gels on the fingers.
Cortisol is highest in the early morning, so samples are usually taken at around 9am.