Cortisol test: what it measures, normal morning levels, and the symptoms of high or low cortisol

The test measures total cortisol in the blood — the hormone the adrenal cortex releases in response to ACTH from the pituitary gland. Cortisol raises blood sugar, tempers inflammation, maintains blood pressure and helps the body respond to illness and stress. About 90% of it travels bound to cortisol-binding globulin (CBG) and albumin; the serum test counts the bound and free fractions together, which matters when a medication changes the amount of binding protein.

Cortisol follows a strong circadian rhythm: it is highest in the hour or two after waking, falls through the afternoon and reaches its lowest point around midnight. A result only means something when the draw time is known, which is why TestWell's cortisol test is a morning draw and the reference range is written for 6–10 a.m. The same number at 4 p.m. would be read very differently.

A morning serum cortisol is not the same as a cortisol saliva test, a 24-hour urine free cortisol or a dexamethasone suppression test. Those measure the free hormone, the day's total output, or the adrenal glands' response to suppression, and they are the tests endocrinologists use to confirm excess cortisol. The blood test is the screening tool for too little cortisol and a starting point for too much.

Low cortisol — adrenal insufficiency — is uncommon but serious, and its symptoms are gradual and nonspecific:

An adrenal crisis — severe vomiting, confusion, very low blood pressure and collapse — is a medical emergency, usually triggered by illness or stress in someone whose adrenal glands cannot respond. People who have taken steroid medication (prednisone, high-dose inhaled or injected steroids) for weeks and stopped abruptly are a common group with low cortisol.

A single low morning cortisol does not confirm adrenal insufficiency, and a normal one does not fully exclude it; the ACTH stimulation test is the standard follow-up. Timing matters: cortisol peaks around 8 a.m., and a late-morning draw reads lower.

The strongest reason to test is suspected adrenal insufficiency: unexplained profound fatigue, weight loss, poor appetite, nausea, dizziness on standing, salt craving, low blood pressure or darkening of skin creases and scars. Anyone who has taken glucocorticoid medication for weeks — prednisone tablets, but also high-dose inhaled steroids for asthma, potent topical steroids, or repeated joint injections — can suppress their own cortisol production and is a candidate for testing when those symptoms appear, especially after stopping or tapering the drug.

People also test for the opposite picture: weight gain concentrated in the trunk, face and upper back, purple stretch marks wider than a centimeter, skin that bruises and tears easily, muscle weakness climbing stairs or rising from a chair, new or worsening high blood pressure or blood sugar, insomnia, low mood or irritability, acne and excess facial hair in women, and irregular periods. Together these are the features of Cushing's syndrome, and a morning cortisol is a reasonable first step even though it cannot rule the condition in or out on its own.

Athletes, people under sustained stress and people tracking recovery from burnout sometimes test cortisol as a baseline. A single morning value is a blunt instrument for that purpose — it varies day to day with sleep, illness and the stress of the draw itself — so trends over several draws at the same time of day are more informative than any one result.

Book the draw for 7–9 a.m., ideally within about two hours of waking, and keep your usual sleep schedule the night before. Night-shift workers should tell the reviewing physician, because their peak shifts with their sleep and a 7 a.m. draw may catch the trough instead. No fasting is required for cortisol itself, but avoid intense exercise that morning and try to arrive a few minutes early so the stress of rushing does not inflate the result.

Medications matter more than food. Any glucocorticoid — oral, inhaled, nasal, topical, injected — can lower the body's own cortisol, and prednisone and prednisolone also cross-react in many cortisol immunoassays, producing a falsely high reading. Estrogen-containing birth control and pregnancy roughly double cortisol-binding globulin, which raises total cortisol without changing the free, active hormone; a normal-to-high result on the pill is expected, not alarming. List every steroid-containing product and any hormonal contraception when you order.

You can order the morning cortisol test online through TestWell: a physician reviews and approves the order, you visit a Quest or Labcorp patient service center (BioReference in New York and New Jersey) first thing in the morning, and the result appears in your portal within a few business days with the 6–10 a.m. reference range printed alongside it.

For a draw between 6 and 10 a.m., the reference range TestWell's catalog uses is 6.2–19.4 mcg/dL (about 170–535 nmol/L). Ranges differ slightly between laboratories and assay methods, so read your result against the range printed on your own report. Afternoon values run roughly half the morning value, and a healthy midnight level is very low.

Interpretation is asymmetric. At the low end, the Endocrine Society's adrenal-insufficiency guideline treats a morning cortisol below about 3 mcg/dL as strongly suggestive of adrenal insufficiency and a value above about 15 mcg/dL as making it unlikely; results in between need an ACTH stimulation test to settle the question. At the high end, there is no single blood value that diagnoses Cushing's syndrome — because the normal morning range is wide and stress, illness and estrogen push results upward, a high morning cortisol is common in perfectly healthy people and the confirmatory tests measure cortisol differently.

The signs of sustained high cortisol build slowly. The most recognisable are weight gain around the abdomen, face and the back of the neck while arms and legs stay thin; a rounded, reddened face; wide purple stretch marks on the abdomen, thighs or arms; thin skin that bruises with minor knocks and heals slowly; weakness in the shoulder and hip muscles; and high blood pressure or high blood sugar that appears or worsens without an obvious reason. Less visible are insomnia, anxiety, depression or irritability, poor concentration, frequent infections, and in women acne, extra facial hair and irregular or absent periods. In children the first sign is often slowed growth alongside weight gain.

Most high cortisol results do not have Cushing's syndrome behind them. Acute stress, a poor night's sleep, an infection, pain, intense exercise, alcohol, depression and obesity all raise cortisol, as does the stress of the blood draw. Estrogen-containing contraceptives and pregnancy raise the total level by increasing binding protein. Glucocorticoid medication is the most common cause of genuine cortisol-excess symptoms — the body is receiving cortisol-like hormone from the drug — and it paradoxically suppresses the body's own production, so the blood level can read low, high or normal depending on the drug and the assay.

Endogenous Cushing's syndrome — the body making too much cortisol on its own — is rare, on the order of a few cases per million people per year. It is caused by a cortisol-producing adrenal tumor, an ACTH-producing pituitary tumor (Cushing's disease), or, rarely, ACTH from a tumor elsewhere. Because it is rare and the morning blood test is a poor discriminator, the Endocrine Society recommends screening people with suggestive features using late-night salivary cortisol, the 1 mg overnight dexamethasone suppression test or 24-hour urinary free cortisol — usually two of them, repeated — rather than a serum cortisol alone.

A low morning cortisol is the more urgent finding. Adrenal insufficiency means the adrenal glands cannot make enough cortisol, either because the glands themselves are damaged (primary adrenal insufficiency, or Addison's disease — usually autoimmune) or because the pituitary is not sending enough ACTH (secondary). The most common cause overall is suppression of the pituitary–adrenal axis by glucocorticoid medication, which can persist for weeks to months after the drug is stopped.

Symptoms are non-specific and easy to attribute to stress or a virus: deep fatigue, weakness, nausea, poor appetite and weight loss, abdominal pain, dizziness on standing, salt craving, low blood pressure and, in primary disease, darkened skin over knuckles, creases and scars. Blood tests may also show low sodium, high potassium and low glucose. Untreated, an intercurrent illness can tip adrenal insufficiency into adrenal crisis — vomiting, confusion, collapse — which is a medical emergency.

A morning cortisol below about 3 mcg/dL, or a low-normal value with these symptoms, is followed by an ACTH level and an ACTH (cosyntropin) stimulation test, which shows whether the glands can respond. Anyone with a low result who feels unwell should be seen promptly rather than waiting for a routine appointment.

A single high morning cortisol without any features of Cushing's is usually repeated under calmer conditions — after a normal night's sleep, off oral estrogen if that is practical, with the draw taken within two hours of waking. If it stays high or the physical signs are present, the next step is one of the screening tests above, ordered and interpreted by a clinician, followed by ACTH and imaging only if excess is confirmed. Glucose, potassium and blood pressure are checked along the way because they are where cortisol excess does its damage.

A low result is confirmed and localised with ACTH and a stimulation test, plus sodium, potassium and glucose, and every steroid-containing medication is reviewed. Confirmed adrenal insufficiency is treated with replacement hydrocortisone, with sick-day rules and an emergency injection kit; it is a lifelong, manageable condition once recognised. Either way, cortisol is one number in a rhythm — the pattern across the day and the response to stimulation or suppression are what clinicians act on, and a morning draw is the first data point rather than the last word.