What the value means
Blood cortisol is reported in nmol/L and follows a strong daily rhythm: it rises during the second half of the night, peaks about 30–45 minutes after waking and falls to its lowest in the evening. Morning reference ranges differ between laboratories and depend on the time of the draw and the method. A higher morning cortisol is often a normal response in healthy people. From a prevention point of view, the whole daily pattern, your sleep and how you feel say more than one number above the limit.
Possible causes
- Timing and the draw itself – a draw shortly after waking, rushing, needle anxiety or a stressful wait will raise the value.
- Poor or short sleep – sleep deprivation, night shifts or jet lag shift the daily cortisol rhythm.
- Estrogens and pregnancy – hormonal contraception and pregnancy increase the binding protein, so total blood cortisol is higher.
- Medicines and substances – corticosteroids (including creams and inhalers) can distort the result; alcohol, intense training and fasting also play a role.
- Long-term strain and illness – persistent stress, depression, obesity or, rarely, Cushing's syndrome can lead to persistently raised cortisol.
What you can do
- Repeat the test – draw between 7 and 9 a.m., after a calm night, seated after a short rest; note when you woke up and when blood was taken.
- Ask about targeted tests – if excess cortisol is suspected, doctors use late-night salivary cortisol, 24-hour urinary cortisol or a dexamethasone suppression test.
- Regular sleep – consistent bed and wake times, morning daylight and a dark bedroom support a healthy rhythm.
- Managing stress – exercise, time in nature, breathing exercises and limiting caffeine in the afternoon have reasonable evidence; evidence for “adaptogens” is rather weak.
- Don't chase “adrenal fatigue” – it is not a recognised diagnosis; it is more useful to look for a specific cause of your symptoms.
When to see a doctor
See a doctor if cortisol is repeatedly high and symptoms appear such as weight gain mainly on the abdomen and face, purple stretch marks, easy bruising, muscle weakness, high blood pressure or high blood sugar. Also seek help for long-lasting insomnia, anxiety or depression. If you take corticosteroids, do not stop them – stopping suddenly can be dangerous.