1020. Cortisol (serum)

Cortisol is a steroid hormone synthesized by the adrenal glands. It is widely known as the “stress hormone”. Most cortisol is bound to protein, while a small percentage is “free” and biologically active. Serum cortisol represents total cortisol.

Cortisol levels are highest early in the morning, then decrease throughout the day, with the lowest levels around midnight. This rhythm changes in diseases of the adrenal glands and the pituitary gland. It is optimal to test together with ACTH and other parameters.

Cortisoll is a glucocorticoid (constituting 75–90% of all plasma glucocorticoids), synthesized in the zona fasciculata of the adrenal cortex from cholesterol. It plays a key role in glucose metabolism and the body’s stress response. Cortisol levels are regulated by ACTH, which is synthesized by the pituitary gland in response to corticotropin-releasing hormone and secreted cyclically by the hypothalamus, resulting in peak concentrations (6–8 a.m. being the highest level; 11 p.m. the lowest ACTH and cortisol levels in plasma).

More than 90% of cortisol circulates in the blood bound to corticosteroid-binding globulin and albumin. Less than 5% of circulating cortisol is the free (unbound) form of the hormone. It is filtered in the renal glomeruli and excreted in the urine in its free form.

Serum cortisol represents total cortisol, of which less than 5% is free hormone that exerts the full spectrum of biological effects. An increase in corticosteroid-binding globulin (CBG) concentration leads to elevation of plasma cortisol levels. Increased CBG concentration is caused by hyperthyroidism, diabetes, several hematologic diseases, estrogen therapy, and pregnancy. Normalization of cortisol levels after childbirth or discontinuation of contraceptives may take up to 6 weeks.

A decrease in the concentration of this transport protein is observed in hypothyroidism, liver diseases, nephrotic syndrome, multiple myeloma, and obesity. Any change in CBG concentration leads to a corresponding change in total cortisol levels in the blood.

• Numerous and progressive symptoms characteristic of Cushing’s syndrome / disease (obesity, arterial hypertension, hyperglycemia, myopathy, hirsutism, plethora, osteoporosis, pathological fractures, red striae, increased skin and soft-tissue fragility, menstrual irregularities).
• Atypical clinical symptoms for the patient’s age (osteoporosis, arterial hypertension).
• In children with growth retardation and excessive weight.
• Adrenal incidentaloma with imaging features of an adenoma.
• Differential diagnosis of primary and secondary adrenal insufficiency when assessed together with ACTH.

• Venous blood

In order to exclude factors that may affect the test results, we recommend to follow the preparation rules: