Cortisol

Norm
Morning (8–9 am) 190–690 nmol/l
Afternoon (3–4 pm) half of the morning value
ACTH stimulation increases 3–5 times
Dexamethasone suppression decreases 3–5 times

Synonyms: hydrocortisone
Serum, plasma heparin
Cap is red or green

Measuring serum and urine cortisol and ACTH concentrations are three main indicators used to diagnose Cushing’s syndrome and Cushing’s disease. Determining cortisol concentration involves examining adrenal cortex function. The adrenal cortex secretes cortisol, a glucocorticoid hormone. By the age of three, the daily rhythm of cortisol secretion forms, strongly influenced by the light-dark cycle. Blood cortisol concentration peaks in the morning, making it essential to perform tests at the same time, typically at 8 am. Symptoms such as weight gain, hypertension, impaired glucose tolerance, oligomenorrhea, amenorrhea, and hirsutism may indicate Cushing’s syndrome. Increased cortisol concentration in the blood and daily urine is one of the most important diagnostic factors. Adrenal cortex hyperplasia, adrenal adenoma, and cancer cause Cushing’s syndrome and cortisol hypersecretion. Cushing’s disease involves excess ACTH in the pituitary gland. Random cortisol concentration testing can mislead, especially if emotional stress, hypoglycemia, pregnancy, or daily fluctuations in rhythm are not considered.

Detecting an increase in cortisol concentration suggests the next step could be the dexamethasone suppression test (DST). DST helps determine the cause of elevated cortisol concentration. Dexamethasone, a synthetic steroid, suppresses ACTH secretion and acts as a cortisol analog. If dexamethasone injection reduces elevated cortisol concentration, a feedback connection between the pituitary and adrenal glands is evident, allowing the ruling out of Cushing’s syndrome. An adrenal tumor as the cause of increased cortisol concentration means the dexamethasone suppression test has no effect. Recently, the CRH (corticotropin-releasing hormone) stimulation test has also been used, similar to DST but utilizing a hypothalamic factor. The CRH (Cosyntropin test, Cortrosyn test) stimulation test is superior to DST.

Cortisol accounts for 75–90% of all blood glucocorticoids. In the blood, cortisol binds to albumin and transcortin, with less than 5% of total cortisol biologically active. The liver metabolizes cortisol, which has a half-life of 80–110 minutes, and its metabolites are later excreted in the urine. Cortisol concentration heavily depends on the functional status of other hormones. Blocking cortisol synthesis for any reason quickly increases ACTH concentration in the blood. For diagnosing Cushing’s syndrome, measuring free cortisol in urine is more reliable than measuring it in the blood.

Source | Handbook of Basic Laboratory Tests | Doctor of Medical Sciences Gintaras Zaleskis