Glossary
Cortisol testing, in plain English
36 terms you will meet on test reports, in research and on this site.
- ACTH (adrenocorticotropic hormone)
- The hormone the pituitary gland releases to tell the adrenal glands to make cortisol. Measured alongside cortisol to work out where a problem starts.
- Addison's disease
- Primary adrenal insufficiency: the adrenal glands themselves are damaged, most often by the immune system, and cannot make enough cortisol (and usually aldosterone). Read more
- Adrenal crisis
- A life-threatening drop in cortisol, often triggered by illness, injury or stopping steroids suddenly. Causes severe vomiting, weakness, confusion and collapse. A medical emergency. Read more
- Adrenal fatigue
- A popular term for tiredness blamed on "worn-out" adrenal glands. It is not a recognised medical diagnosis, and reviews have found no evidence for it. Read more
- Adrenal glands
- Two small glands, one on top of each kidney, that make cortisol, aldosterone, adrenaline and some sex hormones.
- Adrenal insufficiency
- Any condition in which the body makes too little cortisol. Primary if the adrenal glands are the cause (Addison's disease); secondary or tertiary if the pituitary or hypothalamus is. Read more
- Assay
- The laboratory method used to measure a substance. Different assays can give somewhat different numbers for the same sample, which is why reference ranges are set by each laboratory.
- CBG (cortisol-binding globulin)
- The protein that carries most cortisol in the blood. Oral oestrogen, including many contraceptive pills and some HRT, raises CBG and so raises total blood cortisol. Read more
- Circadian rhythm
- The body's roughly 24-hour clock. Cortisol follows it closely: highest after waking, lowest around midnight. Read more
- Cortisol
- The main glucocorticoid hormone in humans, made by the adrenal glands. It helps control blood sugar, blood pressure, inflammation, the sleep-wake cycle and the response to stress. Read more
- Cortisol awakening response (CAR)
- The sharp rise in cortisol in the 30 to 45 minutes after waking. Measured with saliva samples taken on waking and shortly after. Read more
- Cortisone
- The inactive form of cortisol. The body converts between the two, and some tests (including some hair and dried urine tests) measure both.
- Cushing's syndrome
- Long-term exposure to too much cortisol, from a tumour (Cushing's disease if it is in the pituitary) or, most often, from steroid medicines. Read more
- Cyclic Cushing's
- Cushing's syndrome in which cortisol rises and falls in episodes, so single tests can be normal between them. Research has used segmented hair to build a timeline of these episodes. Read more
- Dexamethasone suppression test
- A test of whether the body turns down its own cortisol when given dexamethasone, a synthetic steroid. Used to screen for Cushing's syndrome. Read more
- DHEA and DHEA-S
- Hormones made by the adrenal glands that are often measured alongside cortisol in stress panels.
- Diurnal
- Varying across the day. Cortisol has a strong diurnal pattern. Read more
- DUTCH test
- Dried Urine Test for Comprehensive Hormones: urine dried on filter paper at several points in one day, measuring cortisol, cortisone and their breakdown products. Read more
- Free cortisol
- The small share of cortisol in the blood, around 4 to 6 per cent, that is not bound to proteins and is active. Saliva and urine tests measure free cortisol.
- µg/dL
- Micrograms per decilitre, the unit for blood cortisol in the US. One µg/dL is 27.59 nmol/L. Read more
- Glucocorticoid
- The class of steroid hormones that includes cortisol, and the medicines that copy it, such as prednisolone, hydrocortisone and dexamethasone.
- Hair cortisol concentration (HCC)
- The amount of cortisol in a hair sample, reported in pg/mg (the same as ng/g). A measure of cortisol exposure over the months the hair grew. Values depend heavily on the laboratory method, so there is no single normal range. Read more
- HPA axis
- The hypothalamic-pituitary-adrenal axis: the chain from the brain (hypothalamus) to the pituitary gland to the adrenal glands that controls cortisol. Read more
- Hydrocortisone
- The medicine form of cortisol, used as replacement for people with adrenal insufficiency and in creams and injections.
- Immunoassay
- A measuring method that uses antibodies to detect a substance. Quick and widely used, but can cross-react with similar molecules.
- Late-night salivary cortisol
- A saliva sample taken at around 11pm, when cortisol should be at its lowest. A first-line screening test for Cushing's syndrome. Read more
- LC-MS/MS
- Liquid chromatography with tandem mass spectrometry: a precise laboratory method that separates and identifies molecules by mass. Often used for hair cortisol. Read more
- nmol/L
- Nanomoles per litre, the unit for blood and urine cortisol in the UK, Europe and Australia. Read more
- pg/mg
- Picograms per milligram, the unit for hair cortisol: the weight of cortisol in each milligram of hair. Read more
- Posterior vertex
- The area at the back of the head, just below the crown, where hair samples are cut because results vary least between neighbouring samples there. Read more
- Reference range
- The range of results found in most healthy people, set by each laboratory for its own method. Being outside it is a prompt to look further, not a diagnosis. Read more
- Segmental analysis
- Cutting a longer hair sample into short sections, usually 1 cm each, and testing each one to see cortisol month by month. Read more
- Synacthen test (ACTH stimulation test)
- A blood test of how well the adrenal glands respond to a dose of synthetic ACTH. The standard test for adrenal insufficiency. Read more
- Total cortisol
- All the cortisol in the blood, bound and free. What a standard blood test measures. Read more
- Urinary free cortisol (UFC)
- The free cortisol passed in urine over 24 hours. A first-line screening test for Cushing's syndrome. Read more
- Washout effect
- The gradual loss of cortisol from hair further from the scalp, through washing, sunlight and weathering. The reason laboratories test the hair nearest the scalp. Read more