Finding the right tests…
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Finding the right tests…
Hormonal
Cortisol runs on its own daily clock, and it's normally at its highest within an hour or so of waking, which is exactly why this test is drawn in the morning. A single AM cortisol reading helps your doctor start narrowing down whether your adrenal glands are producing too much or too little of the hormone. A morning level that's unexpectedly low points toward Addison's disease or adrenal insufficiency, while a level that's high, especially alongside weight gain and stretch marks, can suggest Cushing's syndrome, though that diagnosis usually needs more than one test. Because cortisol swings through the day, this result only means something read against the expected morning peak. Your doctor may pair it with a PM sample.
This test measures cortisol concentration in a blood sample drawn in the morning, ideally close to when you naturally wake up, since that's when cortisol is normally at its daily peak. A standard venous draw is used. Your doctor will usually want this timed precisely — drawn too late in the morning and the result can look artificially low even in a healthy person — so confirm the exact collection window with the centre before your appointment. It's often ordered alongside an afternoon or evening sample for comparison.
Cortisol doesn't sit at one steady level all day — it follows a rhythm set by your body clock, climbing to its highest point shortly after you wake and tapering off through the rest of the day. Testing it first thing in the morning is what lets your doctor compare your result against that expected peak.
A morning cortisol that's unexpectedly low can point toward your adrenal glands not producing enough of the hormone, as seen in Addison's disease or other forms of adrenal insufficiency, according to MedlinePlus. A morning level that's high, especially with symptoms like weight gain around the midsection, stretch marks, or high blood pressure, is one of several clues NIH's NIDDK describes doctors looking for in Cushing's syndrome.
Neither adrenal insufficiency nor Cushing's syndrome is typically confirmed from a single morning cortisol value. NIDDK notes that doctors usually combine two or more tests, sometimes a same-day afternoon sample, sometimes a stimulation or suppression test, since no single test is considered perfect on its own.
- Timed to your body's natural morning cortisol peak - Rarely diagnostic as a single, stand-alone result - Often paired with an afternoon or evening sample
Cortisol follows a natural daily rhythm and is normally at its highest within an hour or two of waking, according to MedlinePlus, so a morning draw is needed to compare your result against the expected peak.
A low result can point toward Addison's disease or another cause of adrenal insufficiency, according to MedlinePlus, though your doctor will usually confirm with additional testing before making that diagnosis.
A high result is one of several signs doctors look for in Cushing's syndrome, per MedlinePlus and NIH's NIDDK, but a single high reading isn't diagnostic on its own — confirmation usually needs at least one more type of test.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Often, yes. Comparing a morning result against a later same-day sample shows whether cortisol drops the way it normally should, which is a meaningful diagnostic clue described by NIH's NIDDK, particularly for Cushing's syndrome.
Fasting and timing requirements can vary by centre. Ask your doctor or the centre directly when you book to make sure your sample is collected at the right time.
Cortisol is a stress-responsive hormone, so acute stress or a disrupted sleep pattern on the day of testing can affect your level, which is one reason an unusual result is often confirmed with repeat or additional testing.
Morning cortisol is normally at its daily high point, but the exact numeric reference range depends on the lab and assay used. Ranges vary by lab, so ask your doctor to interpret the range printed on your own report.