Cortisol test: morning normal range, results and testing in Dubai

A cortisol test measures cortisol, the stress hormone made by the adrenal glands, usually in a blood sample taken in the morning. Cortisol follows a daily curve, so the time of the draw is part of the result. Despite the nickname, a single morning value is not a stress score: sleep, illness, medicines and the clock all move it. What it can do is flag whether the adrenal glands might be making too much or too little, which a doctor then checks with more specific tests.

What cortisol does

Cortisol is a steroid hormone made by the adrenal glands, which sit on top of the kidneys. It helps the body respond to stress, damps down inflammation, and helps regulate blood sugar, metabolism and blood pressure. The pituitary gland at the base of the brain sets how much is made by releasing ACTH, the hormone that tells the adrenal glands to produce cortisol.

The daily curve

In people with a regular sleep pattern, cortisol starts to rise at around 3 to 4 in the morning, peaks between 7 and 9, then falls through the day to very low levels around midnight. That curve is why a cortisol result means little without a time attached, and why a morning sample is the usual starting point. The Endocrine Society notes that the rhythm is blunted in many people with depression and in shift workers.

What a blood cortisol test measures

In blood, cortisol is partly carried on a binding protein, cortisol-binding globulin (CBG), and a standard blood test measures the total: the bound and the free together. That matters because anything that raises the binding protein raises total cortisol without the body making more. Oestrogen in contraceptive pills does this, and so does pregnancy.

Normal morning cortisol range

MedlinePlus, the US National Library of Medicine's health information service, gives a normal range of 5 to 25 µg/dL (138 to 690 nmol/L) for a blood sample taken at 8 in the morning. Levels are much lower by the afternoon, so a sample taken around 4 p.m. needs a different range. The Endocrine Society stresses that cut-offs should be based on the specific assay, because different methods give different numbers. Read your result against the range on your own report, and check the time the sample was taken.

Who usually asks for a cortisol test

A doctor usually orders cortisol when symptoms suggest the adrenal glands may be making too much or too little. MedlinePlus lists weight gain, a rounded face, easy bruising and muscle weakness as signs that can prompt a check for too much cortisol, and long-lasting tiredness, weight loss and abdominal pain as signs that can prompt a check for too little. It also comes up for people who have taken steroid medicines for a long time, because long-term use, or stopping suddenly, is the most common reason for an abnormal level. Cortisol testing is used to follow known adrenal and pituitary conditions through treatment as well.

Many people now meet morning cortisol as one line in a broad blood panel. There it works as a baseline to compare against later, rather than a test for any particular condition.

Types of cortisol test

• Morning blood cortisol. The common starting test, sometimes paired with a second sample around 4 p.m.
• 24-hour urine cortisol. All urine over a day is collected, giving a picture of total output that is not affected by changes in the binding protein.
• Late-night saliva cortisol. Collected at home late in the evening, when cortisol should be at its lowest.
• Dexamethasone suppression test. A small dose of a steroid tablet at night, then a morning blood sample, to see whether cortisol switches off as expected.
• Corticotropin (ACTH) stimulation test. An injection of synthetic ACTH followed by blood samples, to see whether the adrenal glands can respond. The Endocrine Society calls it the diagnostic standard for primary adrenal insufficiency.

For suspected Cushing's syndrome, the Endocrine Society recommends the urine, late-night saliva or dexamethasone tests, and recommends against using a random blood cortisol to test for it. For the opposite question, too little cortisol, a low morning value is one of the findings that leads a doctor towards a stimulation test.

What a high cortisol usually points to

A high morning result has several everyday explanations to rule out before anything else.

• Stress, illness and exercise. Physical or emotional stress, an acute illness and hard exercise all raise cortisol.
• Oestrogen and pregnancy. Oestrogen-containing contraceptive pills raise the binding protein, and total cortisol with it. In pregnancy, total cortisol rises two- to threefold.
• Steroid medicines. Hydrocortisone, prednisolone and similar medicines can affect the result.
• Pseudo-Cushing's states. Cortisol can run high for a while with depression, anxiety, alcohol use disorder, poorly controlled diabetes or obesity.
• Cushing's syndrome. A tumour in the pituitary, an adrenal gland or elsewhere drives cortisol production. It is diagnosed with the specific tests above, not with a morning blood level.

A doctor who sees a high morning cortisol usually reviews medicines and recent illness, and if the wider picture fits, moves to one of the tests the Endocrine Society recommends.

What a low cortisol usually points to

• Timing. A sample taken later than intended can read low simply because cortisol has already fallen.
• Steroid medicines. Glucocorticoid tablets, creams, eye drops, inhalers and joint injections can suppress the body's own production.
• Addison disease. The adrenal glands themselves make too little, for example after damage from autoimmune disease or certain infections.
• Hypopituitarism. The pituitary does not send enough ACTH.
• Low binding protein. Critical illness, and kidney conditions that leak protein, lower total cortisol.

The Endocrine Society's guideline on adrenal insufficiency suggests a morning cortisol below 140 nmol/L (5 µg/dL), read with ACTH, as a preliminary test when a stimulation test cannot be done, and treats the stimulation test as the diagnostic standard. It also notes that a low sodium and, later, a high potassium often set off the investigation.

What moves cortisol

• The clock and sleep. The daily curve is the largest single factor.
• Shift work and long-haul travel. Shift work blunts the rhythm, and crossing several time zones can throw it out for a while.
• Stress, exercise and illness. All raise cortisol.
• Heat and cold. MedlinePlus lists hot and cold temperatures among the things that affect cortisol.
• Pregnancy, oestrogen and steroid medicines. As above.
• Biotin. Some hormone tests use biotin in their chemistry, and in a small study a biotin dose found in over-the-counter supplements made some of them read falsely high or falsely low.

Preparing for the test

Book an early slot: MedlinePlus gives its range for an 8 a.m. sample, and the Endocrine Society treats 6 to 10 a.m. as the morning window. Avoid vigorous exercise the day before and rest before the draw. Tell the person taking the sample about every medicine you use, including steroid creams, inhalers, eye drops, joint injections and contraceptive pills, as well as any biotin. Do not stop any medicine for the test unless your doctor tells you to. If you work nights, have just flown across time zones or slept at unusual hours, mention that too.

Reading it with the rest of the panel

Morning cortisol says more next to a few other results. DHEA-S is the other adrenal hormone in the panel, and the Endocrine Society notes that a DHEA-S well below the range for age and sex is a useful early sign of primary adrenal insufficiency. Sodium and potassium can shift when the adrenal glands under-produce. Fasting glucose is worth reading beside it too, since cortisol helps regulate blood sugar.

How Clare's panel handles cortisol

Clare's panel includes morning cortisol, measured by the lab. It is collected in the morning because cortisol follows a daily curve, and a later sample would mean something different. When Clare opens, the result will sit beside your other markers in one account, with a plain explanation that describes what it usually means and does not diagnose.

Why it matters in the UAE

Ramadan changes when people eat and sleep, and cortisol follows the body clock. In a study of 24 healthy adults in Jeddah, the usual gap between morning and evening cortisol disappeared two weeks into Ramadan: evening cortisol was higher than in the month before, and the morning-to-evening ratio fell. A study of 57 overweight and obese adults in Sharjah, which measured saliva cortisol at midday, found no change by the end of Ramadan. The two measured different things at different times of day, but together they make the point that a cortisol taken during Ramadan, or after a night of shifted sleep, is worth flagging to whoever reads it.

Related tests

Morning cortisol is read with DHEA-S, Sodium and Potassium, and Fasting Glucose. Our guide to a comprehensive blood test in Dubai explains why cortisol and other hormones are booked as morning draws.

Why cortisol means more over time

Because cortisol moves with the clock, sleep and circumstances, two results are comparable when they are taken the same way: at the same time of morning, after a normal night, outside an acute illness. Setting a morning value against an afternoon one says little, while a stable result across repeats taken the same way says more than any single reading. Clare is opening with a waitlist at clare.health.