Cortisol
Code:
COR
Sample Type:
Serum (Gold Top)
Minimum volume: 1 mL
Ref Ranges/Units:
Morning (6-10am) range 172 – 497 nmol/L
Mid-afternoon (4-8pm) range 74 – 286 nmol/L
A result <50 nmol/L is phoned to the requesting clinician (unless the clinical details indicate it is DST)
In a DST, expect cortisol to suppress <50 nmol/L
In a SST, expect cortisol to increase >420 nmol/L
A result <250 nmol/L as part of a SST is phoned to the requesting clinician.
Turnaround:
Same Day (60 minutes from receipt for Urgent Samples).
Stability:
24 hours at 20‑25 °C
4 days at 2‑8 °C
12 months at ‑20 °C
Freeze only once.
Special Precautions/Comments:
Ideally take sample at 9am (when cortisol is at its highest).
Additional Information:
Cortisol is a glucocorticoid produced by the cortex of the adrenal gland as part of the hypothalamic-pituitary-adrenal (HPA) axis. Corticotropin-releasing hormone (CRH) from the hypothalamus stimulates the pituitary to secrete adrenocorticotropic hormone (ACTH) which acts on the adrenal gland to produce cortisol. ACTH is also released in response to stress. Cortisol secretion is subject to diurnal variation and is highest at 9am and lowest at midnight (this pattern may be different in shift workers). As such, cortisol measurement is recommended at 9am to aid interpretation. The majority (90%) of circulating cortisol is bound to cortisol binding globulin (CBG) or albumin. Cortisol has many important functions and widespread action including regulating blood pressure, glucose homeostasis, lipid metabolism, bone metabolism and the body’s stress response.
A raised serum cortisol is expected in an acutely ill patient due to stress-induced ACTH secretion. A raised serum cortisol in a non-acutely ill patient may indicate Cushing’s syndrome. Symptoms of Cushing’s syndrome include obesity, buffalo hump, moon face, purple striae, hypertension, osteoporosis, hirsutism, oligomenorrhoea/amenorrhoea and depression. Cushing’s syndrome is investigated using at least 2 of the following investigations: urine free cortisol, an overnight dexamethasone suppression test (DST) or a midnight salivary cortisol.
A low serum cortisol may indicate adrenal insufficiency, such as Addison’s disease. A random cortisol measurement (not 9am) is only useful to exclude adrenal insufficiency and is often measured in the investigation of hyponatraemia. Symptoms of adrenal insufficiency include fatigue, weight loss, hypotension, postural dizziness, anorexia, hyperpigmentation (Addison’s only) and loss of body hair. Low serum cortisol can also be caused by hypopituitarism, where the adrenal is not receiving any stimulation from the pituitary. Adrenal insufficiency can be investigated using a short synACTHen test (SST) and by measurement of ACTH. Low serum cortisol can also be caused by steroid use due to suppression of the HPA axis.
South of Tyne & Wear Pathology Centre
