⚠️ Educational only. LabPlain does not provide medical advice or diagnosis. Always discuss your specific results with your healthcare provider.
What this test measures
Cortisol is your body's primary stress hormone, produced by the adrenal glands — two small glands that sit on top of your kidneys. When you face stress, danger, or even just wake up in the morning, your brain signals the adrenal glands to release cortisol.
Beyond stress, cortisol plays a critical role in regulating your metabolism (how your body uses fat, protein, and carbohydrates for energy), controlling blood pressure, reducing inflammation, and managing your sleep-wake cycle. It's also essential for your immune system — too much suppresses it, too little leaves you vulnerable.
Doctors order a cortisol test when they suspect problems with the adrenal glands or pituitary gland, or when evaluating conditions like Cushing's syndrome or Addison's disease.
Cortisol follows a strong daily rhythm called a diurnal pattern — it peaks in the early morning and drops to its lowest point around midnight. This is why the timing of your blood draw is critical. A result that looks "high" in the afternoon may be perfectly normal in the morning, and vice versa.
Reference ranges also vary between labs. Always compare your result to the range printed on your specific lab report.
⏰ Why timing matters
Most cortisol tests are done at 8 AM — when levels are naturally highest and most consistent between people. If your test was done at a different time, your doctor will interpret the result differently. Always note the time of your blood draw when discussing results.
What your result might indicate
↑ If High
Elevated cortisol may point to chronic stress, Cushing's syndrome, obesity, depression, or overuse of steroid medications. A single high result doesn't confirm a diagnosis — your doctor will likely order follow-up testing.
↓ If Low
Low cortisol may suggest adrenal insufficiency (Addison's disease), hypopituitarism, or recent use of corticosteroid medications that suppressed natural production. Low cortisol can be serious and usually warrants further investigation.
Symptoms associated with abnormal cortisol
↑ High Cortisol Symptoms
Weight gain, especially in the abdomen and face
High blood pressure
Easy bruising or thin skin
Muscle weakness
High blood sugar or diabetes
Anxiety, irritability, or depression
Poor sleep or insomnia
Frequent infections
↓ Low Cortisol Symptoms
Severe fatigue and weakness
Unexplained weight loss
Low blood pressure
Dizziness when standing up
Salt cravings
Nausea, vomiting, or stomach pain
Darkening of skin (Addison's)
Brain fog or difficulty concentrating
Common causes of abnormal cortisol
What can raise cortisol?
The most common cause of mildly elevated cortisol is everyday psychological and physical stress — your body can't tell the difference between a work deadline and a genuine threat. Other causes include Cushing's syndrome (where a tumor causes the adrenal glands to overproduce cortisol), long-term use of corticosteroid medications like prednisone, obesity, depression, alcoholism, and poorly controlled type 2 diabetes.
Temporary spikes are also normal — illness, surgery, intense exercise, and even fasting can raise cortisol levels for hours or days.
What can lower cortisol?
Low cortisol most commonly results from Addison's disease (primary adrenal insufficiency), where the adrenal glands are damaged and can't produce enough cortisol. It can also result from hypopituitarism — a problem with the pituitary gland that fails to signal the adrenals properly. Stopping long-term steroid medication abruptly can also cause a sudden drop in cortisol, which is why doctors always taper these medications slowly.
Tests often ordered alongside cortisol
Cortisol is rarely interpreted in isolation. Your doctor may also order:
ACTH (Adrenocorticotropic Hormone) — helps determine if the problem is in the adrenal glands or the pituitary gland
24-hour urine cortisol — measures cortisol output over a full day, more accurate than a single blood draw
Dexamethasone suppression test — used to diagnose Cushing's syndrome
Aldosterone — another adrenal hormone often checked alongside cortisol
A single abnormal cortisol result is rarely the whole story. Cortisol fluctuates throughout the day and is affected by stress, sleep, exercise, and medications — so your doctor will consider your result in context of your symptoms, medical history, and the time of your blood draw. Don't panic over a single number. Only your doctor can interpret your specific result in context of your full health picture.
Questions to ask your doctor
01Was my cortisol drawn at the right time of day, and does the timing affect how you're interpreting it?
02Do my symptoms match what you'd expect from this result?
03Do I need a 24-hour urine cortisol test or an ACTH stimulation test for a more complete picture?
04Could any medications I'm taking be affecting my cortisol level?
05Should I be referred to an endocrinologist?
06If stress is a factor, what lifestyle changes would actually make a difference?
Frequently asked questions
Can stress alone cause high cortisol on a blood test?
Yes. Psychological stress, poor sleep, intense exercise, and even anxiety about the blood draw itself can temporarily raise cortisol. A mildly elevated result doesn't automatically mean a medical condition — your doctor will consider your lifestyle and order repeat testing if needed.
Is a morning cortisol test more accurate?
Morning tests (around 8 AM) are the gold standard because cortisol is most predictable and consistently highest at that time. Afternoon or evening draws are harder to interpret because normal levels vary much more between individuals later in the day.
Can I lower my cortisol naturally?
Lifestyle factors that consistently help reduce cortisol include regular moderate exercise (intense exercise can temporarily raise it), quality sleep, stress reduction techniques like meditation or deep breathing, reducing caffeine and alcohol, and maintaining a healthy weight. These won't fix a medical condition but can help if stress is the primary driver.
What's the difference between a cortisol blood test and a saliva test?
Blood tests are the standard in medical settings and give a precise snapshot of cortisol at a specific moment. Saliva tests (often used in functional medicine) can measure cortisol at multiple points throughout the day to track the daily rhythm, but they're less standardized and not typically used for diagnosing adrenal disorders.
Is Addison's disease serious?
Yes, but it's manageable with the right treatment. Addison's disease is a chronic condition where the adrenal glands don't produce enough cortisol (and often aldosterone). It requires lifelong hormone replacement therapy, but most people with Addison's live full, normal lives with proper treatment and monitoring.